Imaging an isolated water molecule using a single electron wave packet

Proceedings of the National Academy of Sciences, 2005

We present femtosecond midinfrared pump-probe measurements of the molecular motion and energy-transfer dynamics of a water molecule that is enclosed by acetone molecules. These confined water molecules show hydrogen-bond and orientational dynamics that are much slower than in bulk liquid water. This behavior is surprising because the hydrogen bonds to the CAO groups of the acetone molecules are weaker than the hydrogen bonds in bulk water. The energy transfer between the OOH groups of the confined water molecules has a time constant of 1.3 ؎ 0.2 ps, which is >20 times slower than in bulk water. We find that this energy transfer is governed completely by the rate at which hydrogen bonds are broken and reformed, and we identify the short-lived molecular complex that forms the transition state of this process. hydrogen bonding ͉ infrared pump-probe spectroscopy ͉ energy transfer W ater plays an essential role in many chemical and biological processes. Over the last decades, this notion has motivated a lot of work on the dynamical properties of bulk liquid water (1-7). However, the role of water in (bio)chemical processes is often played by a limited number of water molecules in a strongly restricted molecular environment. For example, the stability, structure, and biological function of proteins are largely determined by only a few surrounding layers of water molecules (8). When the water molecules participate directly in a reaction, the number of involved water molecules is even smaller. For example, the proton-pumping function of bacteriorhodopsin involves changes of the hydrogen network that is formed by particular amino acids of the protein and only a few confined water molecules (9-12). Recently, the dynamics of water in restricted environments was studied by comparing the spectral dynamics of an optically excited probe molecule embedded in a hydrated (bio)molecule with the spectral dynamics of the same probe molecule in bulk water (13). The spectral dynamics reflect the collective rearrangement of the solvating water, and were found to be much slower within the hydrated (bio)molecule than in bulk water. In this article, we present a study of the hydrogen-bond and energy-transfer dynamics of individual H 2 O and 1 H 2 HO molecules in a confined environment. In this study, we probed the dynamics of the water molecules directly with femtosecond midinfrared laser pulses that are resonant with the OOH stretch vibrations.

Angewandte Chemie International Edition, 2007

Accurate infrared spectroscopy of protonated water clusters that are prepared in the gas phase has become possible in recent years, thus opening the door to a deeper understanding of the properties of aqueous systems and the hydrated proton, which are of high interest in central areas of chemistry and biology. Several computational studies have appeared in parallel, providing a necessary theoretical basis for the assignment and understanding of the different spectral features. It has been recently demonstrated that the H 5 O 2 + motif, also referred to as the Zundel cation, plays an important role in protonated water clusters of six or more water molecules and, together with the Eigen cation (H 9 O 4 + ), as a limiting structure of the hydrated proton in bulk water. 11] The importance of the hydrated proton and the amount of work devoted to the problem contrast with the fact that the smallest system in which a proton is shared between water molecules, H 5 O 2 + , is not yet completely understood, and an explanation of the most important spectral signatures and the associated dynamics of the cluster is lacking.

1969

Part I Several approximate Hartree-Fock SCF wavefunctions for the ground electronic state of the water molecule have been obtained using an increasing number of multicenter s, p, and d Slater-type atomic orbitals as basis sets. The predicted charge distribution has been extensively tested at each stage by calculating the electric dipole moment, molecular quadrupole moment, diamagnetic shielding, Hellmann-Feynman forces, and electric field gradients at both the hydrogen and the oxygen nuclei. It was found that a carefully optimized minimal basis set suffices to describe the electronic charge distribution adequately except in the vicinity of the oxygen nucleus. Our calculations indicate, for example, that the correct prediction of the field gradient at this nucleus requires a more flexible linear combination of p-orbitals centered on this nucleus than that in the minimal basis set. Theoretical values for the molecular octopole moment components are also reported. Part II The perturbat...

Nature, 2021

This article is based on the master thesis (Ciftci 2014) related to our invention which is published in World Intellectual Property Organization (WO/2011/048506) as microwave water heater and the theoretical part of whole project. In this article, heating water by microwave (with steady frequency, 2.45 GHz) is analyzed from sub-molecular to Classical Mechanic results of heating. As the aim of this study, we wanted to examine Quantum Mechanical base of heating water by microwave experiments. As a result, we derived a Semi-Quantum Mechanical equation for microwave -water interactions and thus, Wien displacement law can be derived to verify experimental observations by this equation.

Journal of Mathematical Chemistry, 2005

A Gaussian function superposition is described in order to substitute the usual point charge approximation in molecular fixed frames. This procedure avoids the discontinuities at the nuclear positions which haunt first order density and EMP. Total first order density, made of the electronic and the Gaussian nuclear charge distributions, can be used to compute and compare molecular fields within quantum similarity techniques.

Chemical Reviews, 2010

Second-Harmonic Scatteringh (SHS) experiments provide a unique approach to probe non-centrosymmetric environments in aqueous media, from bulk solutions to interfaces, living cells and tissue. A central assumption made in analyzing SHS experiments is that the each molecule scatters light according to a constant molecular hyperpolarizability tensor β (2). Here, we investigate the dependence of the molecular hyperpolarizability of water on its environment and internal geometric distortions, in order to test the hypothesis of constant β (2). We use quantum chemistry calculations of the hyperpolarizability of a molecule embedded in point-charge environments obtained from simulations of bulk water. We demonstrate that both the heterogeneity of the solvent configurations and the quantum mechanical fluctuations of the molecular geometry introduce large variations in the non-linear optical response of water. This finding has the potential to change the way SHS experiments are interpreted: in particular, isotopic differences between H 2 O and D 2 O could explain recent SHG scattering observations. Finally, we show that a simple machine-learning framework can predict accurately the fluctuations of the molecular hyperpolarizability. This model accounts for the microscopic inhomogeneity of the solvent and represents a first step towards quantitative modelling of SHS experiments.

Nature Physics, 2010

1 At the transition from the gas to the liquid phase of water a wealth of new phenomena emerge, which are absent for isolated H 2 O molecules. Many of those are important for the existence of life, for astrophysics and atmospheric science. In particular the response to electronic excitation changes completely as more degrees of freedom become available. Here we report on the direct observation of an ultrafast transfer of energy across the hydrogen bridge in (H 2 O) 2 (a so called water dimer). This intermolecular Coulombic decay leads to an ejection of a low energy electron from the molecular neighbor of the initially excited molecule. We observe that this decay is faster than the proton transfer which is usually a prominent pathway in case of electronic excitation of small water clusters and leads to dissociation of the water dimer into two H 2 O + ions. As electrons of low energy (∼ 0.7 eV to 20 eV) have been recently found to efficiently breakup DNA-constituents [1, 2] the observed decay channel might contribute as a source for electrons that can cause radiation damage in biological matter.

Applied Physics B-lasers and Optics, 2004

We describe, using a semiclassical approach, the molecular dynamics of a one-dimensional H2 molecule interacting with a laser, beyond the Born–Oppenheimer approximation. We observe and discuss different molecular behaviors, such as ionization and dissociation.