Molecular Physics

Some 39 lines in the B Werner band of the D 2 molecule were measured using a narrowband tunable extreme-ultraviolet laser source, at an unprecedented accuracy of Á= ¼ 6 Â 10 À8 . The results bear relevance for future use in the calibration of dense classical spectra obtained for the HD and D 2 hydrogen isotopologues.

HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

This article reports a practical synthesis of tert-butyl acetylcarbamate, C 7 H 13 -NO 3 , from N-Boc-thioacetamide and the study of its crystal structure. The reaction proceeds in the presence of natural phosphate as a catalyst, with excellent yield, simple workup and benign environment. The crystal structure was refined using a transferred multipolar atom model. In the crystal, symmetrical pairs of strong N-HÁ Á ÁO hydrogen bonds connect the molecules into dimers with an R 2 2 (8) ring motif. The interactions between neighbouring dimers are mostly van der Waals, between hydrophobic methyl groups. Hirshfeld surface analysis shows the major contributions to the crystal packing are from HÁ Á ÁH (42.6%) and OÁ Á ÁH (26.7%) contacts.

In this paper we propose two schemes of using the so-called QTTapproximation for the solution of multidimensional parabolic problems. First, we present a simple one-step implicit time integration scheme using an ALS-type solver in the QTT-format. As the second approach, we use the global space-time formulation, resulting in a large block linear system, encapsulating all time steps, and solve it at once in the QTT format. We prove the QTT-rank estimate for certain classes of multivariate potentials and respective solutions in (x, t) variables. The log-linear complexity of storage and the solution time is observed in both spatial and time grid sizes. The method is applied to the Fokker-Planck equation arising from the beadssprings models of polymeric liquids.

To date no experiment has reached the level of sensitivity required to observe weak nuclear force induced parity violation (PV) energy differences in chiral molecules. In this paper, we present the approach, adopted at Laboratoire de Physique des Lasers (LPL), to measure frequency differences in the vibrational spectrum of enantiomers. We review different spectroscopic methods developed at LPL leading to the highest resolutions, as well as 20 years of CO 2 laser stabilization work enabling such precise measurements. After a first attempt to observe PV vibrational frequency shifts using sub-Doppler saturated absorption spectroscopy in a cell, we are currently aiming at an experiment based on Doppler-free two-photon Ramsey interferometry on a supersonic beam. We report on our latest progress towards observing PV with chiral organo-metallic complexes containing a heavy rhenium atom.

Quantifying an atom's transferability, in a force field context, demands a quantitative understanding of how an atom 'experiences' the surrounding environment both intra-atomically and interatomically. Here we investigate the intra-atomic (E intra A ) viewpoint through the study of the atoms C α , H α , N, O, and S in a series of 'mono'-, tri-and penta-peptides. The remaining inter-atomic viewpoint consists of an electrostatic (via multipole moments), exchange and correlation components respectively, of which the electrostatic component has been previously reported. Together these four energy components, as calculated from the Interacting Quantum Atoms (IQA) partitioning approach, express the foundation of the Quantum Chemical Topological Force Field (QCTFF). In order to have transferability within a force field, smaller sample systems must be calculated and developed as representative of larger target systems. The C α , H α , N, O and S atoms in a tri-peptide are energetically comparable to those in their pentapeptide configurations, within 2.1 kJ/mol in absolute value (1 exception). Across all five elements, this energy difference is on average ∼0.3 kJ/mol. On average, the tri-peptide sample systems represent a ∼8.2 Å atomic horizon around the central atoms of interest. Thus, both the previous knowledge of the ∼10.3 Å horizon sphere and ∼0.4 kJ/mol error required by the electrostatic multipole moments, determine how two of the four key QCTFF energy components are affected by an atom's molecular environment. Dedication: It is a pleasure to contribute to a special issue in honour of Andreas Savin, a most generous host with whom I have enjoyed several discussions. As a deep and valiant thinker, a true scientist such as Andreas will surely continue to work in this capacity beyond his official retirement.

We present here a review of the fundamental topics of Hartree-Fock theory in Quantum Chemistry. From the molecular Hamiltonian, using and discussing the Born-Oppenheimer approximation, we arrive to the Hartree and Hartree-Fock equations for the electronic problem. Special emphasis is placed in the most relevant mathematical aspects of the theoretical derivation of the final equations, as well as in the results regarding the existence and uniqueness of their solutions. All Hartree-Fock versions with different spin restrictions are systematically extracted from the general case, thus providing a unifying framework. Then, the discretization of the one-electron orbitals space is reviewed and the Roothaan-Hall formalism introduced. This leads to a exposition of the basic underlying concepts related to the construction and selection of Gaussian basis sets, focusing in algorithmic efficiency issues. Finally, we close the review with a section in which the most relevant modern developments (specially those related to the design of linear-scaling methods) are commented and linked to the issues discussed. The whole work is intentionally introductory and rather self-contained, so that it may be useful for non experts that aim to use quantum chemical methods in interdisciplinary applications. Moreover, much material that is found scattered in the literature has been put together here to facilitate comprehension and to serve as a handy reference.

The C-C bond dissociation channel of the ethyl (CH3-CH2) radical is investigated at 197.4, 199.98 and 201 nm by velocity map imaging and resonance enhanced multiphoton ionization (REMPI) detection of the produced CH3 fragments. On the light of high level ab initio calculations performed in this work, up to four dissociation pathways are identified leading, respectively, to ground state CH3 radicals in correlation with CH2 fragments in the first four electronic states. The major pathway is associated to threshold dissociation over an exit barrier located at the point of a conical intersection between the initially populated 3p A state and a dissociative valence state. As discussed in the text, the concomitance of both features opens the narrow window in which C-C bond dissociation occurs for ethyl and, presumably, for other similar alkyl radicals.

We report the emergence of dark-excitons in transition-metal-dichalcogenide (TMD) heterostructures that strongly rely on the stacking sequence, i.e., momentum-dark K-Q exciton located exclusively at the top layer of the heterostructure. The feature stems from band renormalization and is distinct from those of typical neutral excitons or trions, regardless of materials, substrates, and even homogeneous bilayers, which is further confirmed by scanning tunneling spectroscopy. To understand the unusual stacking sequence, we introduce the excitonic Elliot formula by imposing strain exclusively on the top layer that could be a consequence of the stacking process. We further find that the intensity ratio of Q- to K-excitons in the same layer is inversely proportional to laser power, unlike for conventional K-K excitons. This can be a metric for engineering the intensity of dark K-Q excitons in TMD heterostructures, which could be useful for optical power switches in solar panels.

Optically controlled non-equilibrium solvation dynamics in condensed phase have been studied extensively both experimentally and theoretically. The main drawback of linear response theory (LRT) and other existing theories is that they are unable to elucidate the dependence of non-equilibrium solvation time correlation function, S(t), on the excitation wavelength, as observed in the experiment. In order to explain the experimental observation, we first develop a kinetic equation in 1D solvation coordinate (SC) space and then we propose a new perturbative method to derive an analytical expression for S(t) for an anharmonic potential in SC space. We observe from the result of S(t) that the calculated results of the same depend strongly on the innumerable optical states through excitation wavelength, when the potential is anharmonic in SC space, indicating the breakdown of LRT. We have shown that both excitation wavelength and rotational relaxation time carry the information of micro-heterogeneity. Another significant aspect of our work is that the analytical expression obtained for S(t) corresponding to the anharmonic potential decays multi-exponentially, whereas S(t) decays single exponentially for a harmonic potential. More significantly, the calculated results for S(t) are found to be in excellent agreement with the available experimental results for the heterogeneous system.

HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Author suggests and analyzes new universal trapping method of comparatively slow-speed particles of a rarefied gas medium in the potential well induced by the nonhomogeneous electromagnetic field increasing with time (up to some moment). Given method is especially effective at inelastic collisions of particles with walls of the gas cell when necessary preliminary slowdown of particles is possible for their following capture even to a highly shallow potential depth. Corresponding sufficiently compact and simple electromagnetic traps may be used for capture and accumulation not only slow-speed micro-and nano-particles in the high vacuum but also atoms and molecules of a rarefied gas in a cell.

Author suggests and analyzes new universal trapping method of comparatively slow-speed particles of a rarefied gas medium in the potential well induced by the nonhomogeneous electromagnetic field increasing with time (up to some moment). Given method is especially effective at inelastic collisions of particles with walls of the gas cell when necessary preliminary slowdown of particles is possible for their following capture even to a highly shallow potential depth. Corresponding sufficiently compact and simple electromagnetic traps may be used for capture and accumulation not only slow-speed micro-and nano-particles in the high vacuum but also atoms and molecules of a rarefied gas in a cell.

This article examined the differential cross-section and the integral
cross-section (DCS & ICS) for NFx molecules (where x: 1, 2, 3). The
molecules underwent electron collisions (elastic scattering) within a
defined energy range. A theoretical model has been employed to
compute DCS and ICS at specific energies ranging from 1.5 eV to 100
eV. Overall, our DCS findings consistently aligned with measurements
from other researchers; however, theoretical investigations on these
compounds were limited

This study investigates the elastic scattering of electrons and positrons by carbon dioxide (CO 2 ) molecules over a wide energy range from 1 eV to 1 KeV. We have computed differential and integral elastic cross-sections (DCS and ICS) using partial wave analysis and compared the theoretical results with available experimental data. Our findings show a strong correlation with experimental results, particularly at mid to high-energy ranges, validating the employed theoretical frameworks. Additionally, the Sherman function was examined to explore spin polarisation effects during scattering events. This research provides crucial insights for applications in atmospheric physics, materials science, and molecular scattering processes, demonstrating its direct relevance to real-world problems and paving the way for further investigation into particle-molecule interactions.

The self-assembly of particles into organized structures is a key feature of living organisms and a major engineering challenge. While it may proceed through the binding of perfectly matched, puzzle-piece-like particles, many other instances involve ill-fitting particles that must deform to fit together. These include some pathological proteins, which have a known propensity to form fibrous aggregates. Despite this observation, the general relationship between the individual characteristics of the particles and the overall structure of the aggregate is not understood. To elucidate it, we analytically and numerically study the selfassembly of two-dimensional, deformable ill-fitting particles. We find that moderately sticky particles tend to form equilibrium self-limited aggregates whose size is set by an elastic boundary layer associated with collective deformations that may extend over many particles. Particles with a soft internal deformation mode thus give rise to large aggregates. In addition, when the particles are incompressible, their aggregates tend to be anisotropic and fiberlike. Our results are preserved in a more complex particle model with randomly chosen elastic properties. This indicates that generic proteinlike characteristics such as allostery and incompressibility could favor the formation of fibers in protein aggregation, and suggests design principles for artificial self-assembling structures.

Record-breaking magnetic exchange interactions have previously been reported for 3d-metal dimers of the form [M(Pt(SAc) 4 )(pyNO 2 )] 2 (M = Ni or Co) that are linked in the solid state via metallophilic Pt/Pt bridges. This contrasts the terminally capped monomers [M(Pt(SAc) 4 )(py) 2 ], for which neither metallophilic bridges nor magnetic exchange interactions are found. Computational modeling has shown that the magnetic exchange interaction is facilitated by the pseudo-closed shell d 8 /d 8 metallophilic interaction between the filled Pt 2+ 5d z 2 orbitals. We present here inelastic neutron scattering experiments on these complexes, wherein the dimers present an oscillatory momentum-transfer-dependence of the magnetic transitions. This allows for the unequivocal experimental assignment of the distance between the coupled ions, which matches exactly the coupling pathway via the metallophilic bridges. Furthermore, we have synthesized and magnetically characterized the isostructural palladium-analogues. The magnetic coupling across the Pd/Pd bridge is found through SQUID-magnetometry and FD-FT THz-EPR spectroscopy to be much weaker than via the Pt/Pt bridge. The weaker coupling is traced to the larger radial extent of the 5d z 2 orbitals compared to that of the 4d z 2 orbitals. The existence of a palladium metallophilic interaction is evaluated computationally from potential surface cuts along the metal stretching direction. Similar behavior is found for the Pd/Pd and Pt/Pt-systems with clear minima along this coordinate and provide estimates for the force constant for this distortion. The estimated M/M stretching frequencies are found to match experimental observed, polarized bands in singlecrystal Raman spectra close to 45 cm -1 . This substantiates the existence of energetically relevant Pd/Pd metallophilic interactions. The unique properties of both Pt 2+ and Pd 2+ constitutes an orthogonal reactivity, which can be utilized for steering both the direction and strength of magnetic interactions.

Non-equilibrium self-assembly is ubiquitous in physico-chemical and biological systems, and manifests itself at different scales, ranging from the molecular to the cosmological. The formation of microtubules, gels, cells and living beings among many others takes place through self-assembly under nonequilibrium conditions. We propose a general thermodynamic non-equilibrium model to understand the formation of assembled structures such as gels and Liesegang patterns and at the same time able to describe the kinetics and the energetics of the structure formation process. The model is supported for a global mechanism to obtain self-assembled structures from building blocks via activation, deactivation, assembly, and disassembly processes. It is proposed that the resulting structures can be characterised by a structural parameter. Our model may contribute to a better understanding of non-equilibrium self-assembly processes and give deeper insight as to how to obtain a specific structural architecture to materials, such as hydrogels which are of great importance in the design of advanced devices and novel materials.

The infrared bar-spectrum of a single ammonia molecule encapsulated in nano-cage C60 fullerene molecule is modelled using the site inclusion model successfully applied to analyze spectra of CO2 isotopologues isolated in rare gas matrix. Calculations show that NH3 can rotate freely on a sphere of radius 0.184 Å around the site centre of the nano-cage and spin freely about its C3 symmetry axis. In the static field inside the cage degenerate ν3 and ν4 vibrational modes are blue shifted and split. When dynamic coupling with translational motion is considered, the spectral signature of the ν2 mode is modified with a higher hindering barrier (2451 cm -1 ), an effective reduced mass (6.569 g.mol -1 ) and a longer tunneling time (55594 ps) for the fundamental level compared to gas-phase values (2047 cm -1 ), (2.563 g.mol -1 ) and (20.85 ps). As a result this mode is red shifted. Moreover, simulation shows that the changes in the bar-spectrum of the latter mode can be used to probe the temperature of the surrounding media in which fullerene is observed.

The energy levels of methane molecule trapped, at low temperature, in small (s) and large (l) nano-cages of cubic sI clathrates are calculated in the Born-Oppenheimer approximation using the Extended Lakhlifi-Dahoo model based on pairwise atom-atom effective interaction potentials. In the s cage, the center of mass of CH 4 exhibits a slightly asymmetrical 3D oscillation motion with small amplitude around the cage center. Two methods were used to calculate the frequencies of such a motion: a 3D harmonic treatment and a 1D Discrete Variable Representation (DVR) treatment in the X, Y and Z directions. They give approximately the same values of, respectively, 133 cm -1 , 108 cm -1 and 120 cm -1 . In the l cage, the oscillations are anharmonic and characterized by large amplitude motions with frequencies of 63 cm -1 , 52 cm -1 and 47 cm -1 . In the s and l nano-cages, the molecule exhibits strongly perturbed rotational motion. The rotational level schemes are quite different from that of the molecular free rotational motion, and for each nano-cage, the obtained levels are described as combination of the free rotation levels.

The energy levels of CO 2 in the small (s) and large (l) nano-cages of cubic sI clathrates are calculated in the Born-Oppenheimer approximation using pairwise atom-atom interaction potentials. In the s cage, the centre of mass of CO 2 oscillates with small amplitudes, asymmetrically about the cage center with harmonic frequencies around 100 cm -1 . In the l cage, oscillations are anharmonic with large amplitude motions in a plane parallel to the hexagonal faces of the cage and the corresponding frequencies are calculated to be 55 cm -1 and 30 cm -1 . Librational harmonic frequencies are calculated at 101.7 cm -1 and 56.0 cm -1 in the s cage and at 27.9 cm -1 and 46.4 cm -1 in the l cage. Results show that the coupling between the CO 2 molecule and the nano-cage is quite different for the low frequency translational, rotational or librational modes and the high frequency vibrational modes, which consequently leads to different relaxation channels.

Systems composed of soft matter (e.g. liquids, polymers, foams, gels, colloids, and most biological materials) are ubiquitous in science and engineering, but molecular simulations of such systems pose particular computational challenges, requiring time and/or ensemble-averaged data to be collected over long simulation trajectories for property evaluation. Performing a molecular simulation of a soft matter system involves multiple steps, which have traditionally been performed by researchers in a 'bespoke' fashion, resulting in many published soft matter simulations not being reproducible based on the information provided in the publications. To address the issue of reproducibility and to provide tools for computational screening, we have been developing the open-source Molecular Simulation and Design Framework (MoSDeF) software suite. In this paper, we propose a set of principles to create Transparent, Reproducible, Usable by others, and Extensible (TRUE) molecular simulations. MoSDeF facilitates the publication and dissemination of TRUE simulations by automating many of the critical steps in molecular simulation, thus enhancing their reproducibilitya. We provide several examples of TRUE molecular simulations: All of the steps involved in creating, running and extracting properties from the simulations are distributed on open-source platforms (within MoSDeF and on GitHub), thus meeting the definition of TRUE simulations.

The structure of unnatural hexapeptides containing three L-valine units and three unnatural α-amino acids ((2R)-methyl aspartic acid, (2S)-methylornitine and modified proline) has been elucidated using H-NMR and IR spectroscopy and conformational analysis based on molecular dynamics (MD) and cluster analysis. The MD analysis, which provides conformer populations and hydrogen-bond lifetimes, is in good agreement with the H-NMR and IR data.

We report high-resolution (δ ν ≤ 0.001 cm -1 ) Fourier Transform Infrared spectra of fluoroform (CHF 3 ) including the pure rotational (far infrared or THz) range (28-65 cm -1 ), the ν 3 fundamental ( ν0 = 700.099 cm -1 ), as well as the associated "hot' band 2ν 3 -ν 3 ( ν0 = 699.295 cm -1 ) and the 'atmospheric window'range 1100-1250 cm -1 containing the strongly coupled polyad of the levels ν 2 , ν 5 and ν 3 + ν 6 , at room temperature and at 120 K using the collisional cooling cell coupled to our Bruker IFS 125 HR prototype (ZP2001) spectrometer and Bruker IFS 125 HR ETH-SLS prototype at the Swiss Light Source providing intense synchrotron radiation. The pure rotational spectra provide new information about the vibrational ground state of CHF 3 , which is useful for further analysis of excited vibrational states. The ν 3 fundamental band is re-investigated together with the corresponding 'hot' band 2ν 3 -ν 3 leading to an extension of the existing line lists up to 4430 transitions with J max = 66 for ν 3 and 1040 transitions with J max = 43 for 2ν 3 -ν 3 . About 6000 transitions were assigned to rovibrational levels in the polyad ν 2 /ν 5 /ν 3 + ν 6 with J max = 63 for ν 2 ( ν0 = 1141.457 cm -1 ), J max = 63 for ν 5 ( ν0 = 1157.335 cm -1 ) and J max = 59 for ν 3 + ν 6 ( ν0 = 1208.771 cm -1 )(K max = J max in each case). The resonance interactions between the ν 2 , ν 5 and ν 3 + ν 6 states have been taken into account providing an accurate set of effective hamiltonian parameters, which reproduce the experimental results with an accuracy close to the experimental uncertainties (with a root mean square deviation d rms = 0.00025 cm -1 ). The analysis is further extended to the ν 4 fundamental ( ν0 = 1377.847 cm -1 ) interacting with 2ν 3 ( ν0 = 1399.394 cm -1 ). The results are discussed in relation to the importance of understanding the spectra of CHF 3 as a greenhouse gas and as part of our large effort to measure and understand the complete spectrum of CHF 3 from the far-infrared to the near-infrared as a prototype for intramolecular quantum dynamics and rovibrational energy redistribution.

Optical frequency-comb spectroscopy has proven a very useful tool for high-resolution molecular spectroscopy. Frequency combs based on quantum-cascade lasers (QCL) offer the possibility to easily explore the mid-infrared spectral range (4 µm to 12 µm), but are characterised by large repetition frequencies ( ∼ 10 GHz) which make them seemingly unsuitable for high-resolution spectroscopy. Here, we present techniques to overcome this limitation. We have employed the combined advantages of high temporal and high spectral resolution to measure the infrared (IR) spectra of CF 4 and CHCl 2 F in pulsed, skimmed supersonic beams. The low rotational temperature of the beams and the narrow expansion cone after the skimmer enabled the recording of spectra of cold samples with high resolution. The spectra cover the range from 1200 cm -1 to 1290 cm -1 and the narrowest lines have a full width at half maximum of 15 MHz, limited by the Doppler effect. The results demonstrate the potential of QCL dual-comb spectroscopy for broadband ( > 60 cm -1 ) acquisition of spectra at high spectral (better than 5•10 -4 cm -1 , 15 MHz) and temporal (better than 4 µs) resolution and high sensitivity in the mid-infrared range. The power of the new technology is demonstrated by comparison with previous results for these molecules obtained by FTIR and diode laser spectroscopy.

The determination of the dielectric properties of polar liquids by computer simulation has, in the past, presented both conceptual and computational difficulties. Many of the conceptual problems have now been at least partially resolved, yet the accurate calculation of the dielectric response for a highly polar liquid remains a major computational task. The usual means of obtaining the static dielectric constant, R, is through the fluctuations in the total dipole moment of the system. In this paper we describe an alternate approach which relies upon the long-range asymptotic behaviour of the dipole-dipole correlations in order to determine g. It requires that a rather large simulation cell be employed, in the present case samples of 4000 particles. Molecular dynamics simulations have been performed for a highly polar fluid composed of dipolar soft spheres in which the dipole-dipole interactions have been evaluated using the Ewald summation technique. Results for the static dielectric constant are reported and compared with previous calculations. The microscopic structure is examined in detail with particular attention being paid to the effects of boundary conditions and numerical implementation. We also consider whether the current understanding of these systems can in fact account for the behaviour observed.

The dielectric response and the electrostriction of polar liquids are certainly important properties of these systems. They also play fundamental roles in processes such as solvation. In this article we report results from a computer simulation study of the behaviour of a highly polar fluid subject to static homogeneous electric fields. Values for three different measures of the dielectric constant are given and their dependences on the field strength analysed. Surprisingly, we find that the integral response and the differential response perpendicular to the field appear to be equal. System size and boundary condition effects are examined; at low fields the behaviour observed reflects that found previously in e 0 , the zero-field static dielectric constant. As expected at small fields, the dielectric constants and the electrostriction exhibit a simple quadratic dependence upon the field strength. We show that even when very large fields are applied the present dipolar soft-sphere fluid does not demonstrate a phase transition similar to the isotropic-to-nematic transition observed by Wei and Patey at zero field for larger dipole couplings.

In this work, we describe the development of a computational screening approach for tripeptide-dipeptide co-assembly. Studies are carried out both in water and in oil-water mixtures, to evaluate possible candidates that give rise to hydrogels or more stable emulsions, respectively, through nanofibre formation. The results give rise to design rules for the identification of promising systems for numerous types of soft materials. The possibility of achieving innovative functional materials through the co-assembly of tripeptides and dipeptides is studied. In particular, coarse-grained simulations allowed for the extraction of some promising dipeptides that, together with H-aspartyl-phenylalanyl-phenylalanine-OH (DFF), are able to act as hydrogelators or emulsifiers with superior characteristics relative to DFF on its own.

The energy levels of CO 2 in the small (s) and large (l) nano-cages of cubic sI clathrates are calculated in the Born-Oppenheimer approximation using pairwise atom-atom interaction potentials. In the s cage, the centre of mass of CO 2 oscillates with small amplitudes, asymmetrically about the cage center with harmonic frequencies around 100 cm -1 . In the l cage, oscillations are anharmonic with large amplitude motions in a plane parallel to the hexagonal faces of the cage and the corresponding frequencies are calculated to be 55 cm -1 and 30 cm -1 . Librational harmonic frequencies are calculated at 101.7 cm -1 and 56.0 cm -1 in the s cage and at 27.9 cm -1 and 46.4 cm -1 in the l cage. Results show that the coupling between the CO 2 molecule and the nano-cage is quite different for the low frequency translational, rotational or librational modes and the high frequency vibrational modes, which consequently leads to different relaxation channels.

The spectral dynamics of photoexcited myoglobin (Mb) and its ligated species have been measured using both single wavelength and broadband continuum probes. Ultrafast spectral relaxation of the deoxy photoproduct involves an initially broadened and red-shifted absorption band, which is observed for all samples studied (deoxyMb, metMb, MbNO, MbCO). These results are consistent with an immediate (sub 100 fs) relaxation to the electronic ground state followed by vibrational equilibration. Relaxation of the "hot" photoproduct spectrum is well described using independent time scales for narrowing (400 fs) and blue shifting (0.4-4 ps) as the system returns to equilibrium. A previous multiple electronic intermediate state model, which is based on single wavelength measurements (Petrich, J. W.; Poyart, C.; Martin, J. L. Biochemistry 1988, 27, 4049), does not adequately explain the observed broadband spectral dynamics, particularly on the blue side of the Soret band (unless still more electronic states are postulated). The vibrational relaxation pathway in Mb is explored by using samples with a modified local heme environment (e.g., His93 f Gly mutation and protoporphyrin IX f porphine substitution). The His93 f Gly mutation experiment demonstrates that the covalent bond between the iron and the proximal histidine has little effect on the overall vibrational relaxation of the "hot" heme. In contrast, the protoporphyrin IX f porphine substitution experiment demonstrates the importance of the van der Waals contacts between the heme and the protein/solvent matrix in cooling the locally hot heme. Finally, we discuss the effects of the observed broadband spectral dynamics on timeresolved resonance Raman intensities and show how the time dependent line shape function plays an important role in the extraction of mode specific vibrational temperatures from the resonance Raman data.

A comparison model based in the Löwdin partitioning technique is used to analyze the differences between the wave function and density functional models. This comparison model provides a tool to understand the structure of both theories and its discrepancies in terms of the subjacent mathematical structure and the variationality required for the energy functional. It is argued that the density functional theory can be compared to the wave-function theory. The wave-function theory provides an explicit form of the exact energy functional for a fermion system from the Full Configuration Interaction approach. The density functional theory can be seen as special cases of Löwdin function that do not satisfy all variational conditions on and also on the term. This analysis shows that ignoring the restrictions imposed by the spin and space symmetry requirements of the solutions when making a variational calculation implies that the correlations expressed by the function will be inconsistent with a function derivable from a spin and space symmetry adapted wave function , even for a closed-shell system. The comparison scheme also provides a new insight in order to achieve a consistent description of the molecular electronic structure of both ground and excited states. Some numerical results are reported.

Following on the recent experimental demonstration of a discrepancy between the nonlinear optical (NLO) behavior of several π-conjugated chromophores and their assumed octupolar symmetry, the authors investigate how geometrical distortions influence the NLO response of multipolar push-pull molecules. Their analytical model is set on a basis of valence-bond and charge-transfer states to estimate the hyperpolarizability of organic and metallo-organic chromophores using the lowest possible number of variables. Since symmetry breakdown changes the definition of the molecular Cartesian framework, tensorial spherical coordinates are implemented. The evolution of the nonlinear molecular anisotropy with possible rotational deviations is then evaluated for two recently studied chromophores. Zero-frequency calculations show that, outside optical resonance, weak geometrical distortions lead to strong anisotropy variations in agreement with experimental data. Their goal is to underscore which m...

Experimental and theoretical studies of the effects of weak radio-frequency electric fields on Rydberg-Stark states with electric dipole moments as large as 10000 D are reported. High-resolution laser spectroscopic studies of Rydberg states with principal quantum number n = 52 and 53 were performed in pulsed supersonic beams of metastable helium with the excited atoms detected by pulsed electric field ionisation. Experiments were carried out in the presence of sinusoidally oscillating electric fields with frequencies of 20 MHz, amplitudes of up to 120 mV/cm, and dc offsets of up to 4.4 V/cm. In weak fields the experimentally recorded spectra are in excellent agreement with the results of calculations carried out using Floquet methods to account for electric dipole couplings in the oscillating fields. This highlights the validity of these techniques for the accurate calculation of the Stark energy level structure in such fields, and the limitations of the calculations in stronger fields where n-mixing and higher-order contributions become important.

Understanding the properties of electronically excited states is a challenging task that becomes increasingly important for numerous applications in chemistry, molecular physics, molecular biology, and materials science. A substantial impact is exerted by the fascinating progress in time-resolved spectroscopy, which leads to a strongly growing demand for theoretical methods to describe the characteristic features of excited states accurately. Whereas for electronic ground state problems of stable molecules the quantum chemical methodology is now so well developed that informed nonexperts can use it efficiently, the situation is entirely different concerning the investigation of excited states. This review is devoted to a specific class of approaches, usually denoted as multireference (MR) methods, the generality of which is needed for solving many spectroscopic or photodynamical problems. However, the understanding and proper application of these MR methods is often found to be diff...

The FT-IR and FT-Raman spectra of 2-phenoxymethylbenzothiazole were recorded and analyzed. The surface enhanced Raman scattering (SERS) spectrum was recorded in a silver colloid. The vibrational wavenumbers of the compound have been computed using the Hartree-Fock/6-31G* basis and compared with the experimental values. The appearance of the Ag-O stretching mode at 237 cm -1 in the SERS spectrum along with theoretically calculated atomic charge density, leads us to suggest that the molecule is adsorbed through the oxygen atom with the molecular plane tilted on the colloidal silver surface. The direction of charge transfer contribution to SERS has been discussed from the frontier orbital theory.

Quantum dots in photonic crystals are interesting because of their potential in quantum information processing 1,2 and as a testbed for cavity quantum electrodynamics. Recent advances in controlling 3,4 and coherent probing of such systems open the possibility of realizing quantum networks originally proposed for atomic systems 7-9 . Here, we demonstrate that non-classical states of light can be coherently generated using a quantum dot strongly coupled to a photonic crystal resonator 10,11 . We show that the capture of a single photon into the cavity affects the probability that a second photon is admitted. This probability drops when the probe is positioned at one of the two energy eigenstates corresponding to the vacuum Rabi splitting, a phenomenon known as photon blockade, the signature of which is photon antibunching 12,13 . In addition, we show that when the probe is positioned between the two eigenstates, the probability of admitting subsequent photons increases, resulting in photon bunching. We call this process photon-induced tunnelling. This system represents an ultimate limit for solid-state nonlinear optics at the single-photon level. Along with demonstrating the generation of non-classical photon states, we propose an implementation of a single-photon transistor 14 in this system. The optical system consists of a self-assembled InAs quantum dot with decay rate γ /2π ≈ 0.1 GHz coupled to a three-hole defect cavity 15 in a two-dimensional GaAs photonic crystal, as described in ref. 5. The quantum-dot/cavity coupling rate g /2π = 16 GHz equals the cavity field decay rate κ/2π = 16 GHz (corresponding to a cavity quality factor Q = 10,000), which puts the system in the strong coupling regime . We first characterize the system in photoluminescence by pumping the structure above the GaAs bandgap. The photoluminescence scans in Fig. show the anticrossing characteristic of strong coupling between the quantum dot and the cavity. Here, the quantum dot is tuned into resonance using local temperature tuning 16 around an average temperature of 20 K maintained in a continuous He flow cryostat. To generate non-classical light, we coherently probe the system with linearly polarized laser beams (Fig. ) and observe the cross-polarized output, as described in our previous work 5 . The cross-polarized set-up enables us to separate the cavity-coupled signal from the direct probe reflection, which is essential for achieving large signal-to-noise ratios needed in autocorrelation measurements.

Exciton-coupled chromophore dimers are an emerging class of optical probes for studies of site-specific biomolecular interactions. Applying accurate theoretical models for the electrostatic coupling of a molecular dimer probe is a key step for simulating its optical properties and analyzing spectroscopic data. In this work, we compare experimental absorbance and circular dichroism (CD) spectra of ‘internally-labeled’ (iCy3)2dimer probes inserted site-specifically into DNA fork constructs to theoretical calculations of the structure and geometry of these exciton-coupled dimers. We compare transition density models of varying levels of approximation to determine conformational parameters of the (iCy3)2dimer-labeled DNA fork constructs. By applying an atomistically detailed transition charge (TQ) model, we can distinguish between dimer conformations in which the stacking and tilt angles between planar iCy3 monomers are varied. A major strength of this approach is that the local conform...

Local fluctuations of the sugar-phosphate backbones and bases of DNA (often called DNA ‘breathing’) play a variety of critical roles in controlling the functional interactions of the DNA genome with the protein complexes that regulate it. Here we present a single-molecule fluorescence method that we have used to measure and characterize such conformational fluctuations at and near biologically important positions in model DNA replication fork constructs labeled with exciton-coupled cyanine [(iCy3)2] dimer probes. Previous work has shown that the constructs that we test here exhibit a broad range of spectral properties at the ensemble level, and these differences can be structurally and dynamically interpreted using our present methodology at the single-molecule level. The (iCy3)2dimer has one symmetric (+) and one anti-symmetric (–) exciton with respective transition dipole moments oriented perpendicular to one another. We excite single molecule samples using a continuous-wave linea...

In strongly magnetized astrophysical plasma systems, magnetic reconnection is believed to be the primary process during which explosive energy release and particle acceleration occur, leading to significant high-energy emission. Past years have witnessed active development of kinetic modeling of relativistic magnetic reconnection, supporting this magnetically dominated scenario. A much less explored issue in studies of relativistic reconnection is the consequence of three-dimensional dynamics, where turbulent structures are naturally generated as various types of instabilities develop. This paper presents a series of three-dimensional, fully-kinetic simulations of relativistic turbulent magnetic reconnection (RTMR) in positron-electron plasmas with system domains much larger than kinetic scales. Our simulations start from a force-free current sheet with several different modes of long wavelength magnetic field perturbations, which drive additional turbulence in the reconnection region. Because of this, the current layer breaks up and the reconnection region quickly evolves into a turbulent layer filled with coherent structures such as flux ropes and current sheets. We find that plasma dynamics in RTMR is vastly different from their 2D counterparts in many aspects. The flux ropes evolve rapidly after their generation, and can be completely disrupted due to the secondary kink instability. This turbulent evolution leads to superdiffusion behavior of magnetic field lines as seen in MHD studies of turbulent reconnection. Meanwhile, nonthermal particle acceleration and energy-release time scale can be very fast and do not strongly depend on the turbulence amplitude. The main acceleration mechanism is a Fermi-like acceleration process supported by the motional electric field, whereas the non-ideal electric field acceleration plays a subdominant role. We also discuss possible observational implications of three-dimensional RTMR in high-energy astrophysics.

Two different yet related topics are discussed: (i) the reduction of palladium (II) in Pd(OAc) 2 complexes reacting with phenyl phosphines and leading to Pd(0) phosphines complexes and (ii) the carbonylation reaction of allyl chlorides catalyzed by these Pd(0) species. The results show that the overall reduction is an exothermic process that can be accomplished along two different reaction paths: one of them is clearly favoured. Similarly, three different channels have been determined for the carbonylation reaction that primarily differ for the timing and the way with which the reacting species bind the metal. In the first path (σ-path), the allyl fragment interacts very weakly with the metal, whereas, successively the CO molecule strongly binds it and reacts with the allyl. A second channel (π-η 3 pathway) is characterized by a π-η 3 interaction between the allyl fragment and the palladium, to which the CO molecule binds, before the two units react affording the product. In both cases, two consecutive migrations of the chlorine "assist" the course of the reaction. In a third case (η 2 pathway) the allyl fragment initially enters the palladium coordination sphere, then the CO molecule simultaneously binds it and the phosphorous atom of one phosphine ligand. The first two paths are favoured.

 With the modified Robert-Bonamy (RB) formalism, the halfwidth  is given by The integrand of  is  Usually, S 2 consists of three terms S 2,outer,I , S 2,outer,f , and S 2,middle . For example, S 2,outer,I is given by  In order to consider more realistic potentials, it is necessary to include a short range atom-atom model V atom-atom (t) () 2 2 2 2 2 2 Re ( ) (1 ).

The X2Σ ground and the A2Π and B2Σ first two excited states of Li-He and Na-He are determined using high level complete active space self-consistent field-multireference configuration interaction ab initio method. The obtained potentials differ from the ones proposed by Pascale [Phys. Rev. A 28, 632 (1983)]10.1103/PhysRevA.28.632, more strongly for the ground than for the excited states. Quantum diffusion Monte Carlo studies of small Li*Hen and Na*Hen with n ⩽ 5 are performed using a diatomics-in-molecule approach to model the non-pair additive interaction potential. The sensitivity of our results to the A2Π and B2Σ potentials used is assessed by an analysis of the structure and of the energetics of the clusters. For these small clusters, the physical conclusions are essentially independent of the diatomic curves employed.

The complete Raman spectra of a single crystal of LiNiPO4 for a wide temperature range are reported. Of the 36 Raman-active modes predicted by group theory, 33 have been detected. The spectra are successfully analyzed in terms of internal modes of the (PO4)3− group and external modes. Multiphonon Raman scattering is also discussed. Low-frequency lines, observed in the antiferromagnetic phase, are assigned to magnon scattering and are discussed briefly.

Scanning tunneling microscopy (STM) and high resolution low-energy electron diffraction measure- ments on vicinal (stepped) Si(111)surfaces reveal mixtures of singleand triple-layer-height steps, with the density of triples increasing with total step density. The diffraction signature of the step mixtures is an incommensurate spacing; however, the STM data show no periodic sequence of singles and triples. Instead, there is a random sequence with specific ratios of the lengths of terraces bounded by steps of different heights, quantitatively consistent with the energetic ground state for elastically interacting steps.

The paper presents infrared reflectivity and micro-Raman scattering spectra of LiBC powder pellets. The experiment allowed assignment of frequencies of all infrared and Raman active zone center modes: E1u(LO) at 1262 cm -1 and 381 cm -1 , E2g at 1172 cm -1 and 174 cm -1 and A2u(LO) at 825 cm -1 and 545 cm -1 . Results are compared with available ab-initio calculations; prediction of large Born effective charges on the nodes of B-C graphene sheets is confirmed.

The growing demand for analytical methods for the detection of biological analytes has stimulated a renewed interest in electrochemical reaction sequences producing electronically excited species prone to emit a photon upon its return to the ground state, a process called Electrogenerated Chemiluminescence (ECL). Both known types of ECL mechanisms, the so called annihilation and co-reactant ECL, are of importance in physical chemistry, but it is the fact that many luminophore/co-reactant pairs may include biological amines as co-reactants that has made ECL the method of choice for bioanalytical purposes owing to its high sensitivity and immunity to noise. In this chapter we present theoretical analyses and approaches for numerical simulation of typical ECL systems of both types that help reveal limiting factors controlling the intensity of ECL emission and ways to quantitatively optimise such systems to enhance their analytical efficiency.

Switchable nonlinear optical (NLO) materials have widespread applications in electronics and optoelectronics. Thermo-switches generate many times higher NLO responses as compared to photo-switches. Herein, we have investigated the geometric, electronic, and nonlinear optical properties of spiropyranes thermochromes via DFT methods. The stabilities of close and open isomers of selected spiropyranes are investigated through relative energies. Electronic properties are studied through frontier molecular orbitals (FMOs) analysis. The lower HOMO-LUMO energy gap and lower excitation energy are observed for open isomers of spiropyranes, which imparts the large first hyperpolarizability value. The delocalization of π-electrons, asymmetric distribution and elongated conjugation system are dominant factors for high hyperpolarizability values of open isomers. For deep understanding, we also analyzed the frequency-dependent hyperpolarizability and refractive index of considered thermochromes. T...

Basis set extrapolations are typically rationalized either from analytical arguments involving the partial-wave or principal expansions of the correlation energy in helium-like systems or from fitting extrapolation parameters to reference energetics for a small(ish) training set. Seeking to avoid both, we explore a third alternative: extracting extrapolation parameters from the requirement that the BSSE (basis set superposition error) should vanish at the complete basis set limit. We find this to be a viable approach provided that the underlying basis sets are not too small and reasonably well balanced. For basis sets not augmented by diffuse functions, BSSE minimization and energy fitting yield quite similar parameters.