Akihiro Morita

Sum frequency generation (SFG) spectroscopy is a powerful experimental technique to probe surface structures. This paper presents a new theoretical mode of nonempirical analysis of SFG spectra for interfacial structures, which considerably generalizes our previous effort (Chem. Phys. 2000, 258, 371), which involved several empirical elements. The method is based on a time correlation function for the frequency-dependent hyperpolarizability, which can be straightforwardly evaluated via molecular

We performed ab initio molecular orbital (MO) calculations of the response kernel (∂Qa/∂Vb), which represents the response of the intramolecular charge polarization by external electrostatic field, on the basis of the coupled perturbed Hartree−Fock equation. The response kernels of some organic molecules including pyrazine, pyrazinyl radical, acetone, and 2-hydroxypropyl radical were calculated along the present formulation. The results revealed that the hydrogen abstraction of pyrazine causes t

This article summarizes the computational analysis of the vibrational sum frequency generation (SFG) spectroscopy with molecular dynamics simulation. The analysis allows direct comparison of experimental SFG spectra and microscopic interface structure obtained by molecular simulation, and thereby obviates empirical fitting procedures of the observed spectra. In the theoretical formulation, the frequency-dependent nonlinear susceptibility of an interface is calculated in two ways, based on the en

Vibrational energy relaxation of azide anion in water was investigated with molecular dynamics simulation. The Landau–Teller formula without the solute electronic polarization exceedingly underestimated the relaxation rate of the antisymmetric stretching mode, and thus various relaxation mechanisms were comprehensively evaluated to elucidate the fast relaxation. As a result, the direct relaxation to the vibrational ground state and the intramolecular vibrational redistribution (IVR) to the symme

When sum frequency generation (SFG) spectroscopy is applied to charged solid/liquid interfaces, the observed SFG signals include both the second-order and third-order polarizations. The latter is called the χ⁽³⁾ effect, which mainly includes induced molecular orientation by electric fields at charged interfaces. We theoretically evaluate the χ⁽³⁾ effect on the SFG spectroscopy of liquid water using molecular dynamics (MD) simulations. The MD simulations enable us to definit

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTSolute-solvent interaction in nonpolar supercritical fluid: a clustering model and size distributionAkihiro. Morita and Okitsugu. KajimotoCite this: J. Phys. Chem. 1990, 94, 16, 6420–6425Publication Date (Print):August 1, 1990Publication History Published online1 May 2002Published inissue 1 August 1990https://pubs.acs.org/doi/10.1021/j100379a048https://doi.org/10.1021/j100379a048research-articleACS PublicationsRequest reuse permissionsArticle Views267A

The present study involves two themes. The first is to incorporate the charge response kernel (∂Qa/∂Vb) into the molecular dynamics simulation, where Qa denotes the partial charge at the site a and Vb the electrostatic potential at the site b. The response kernel was ab initio calculated in our previous study [A. Morita and S. Kato, J. Am. Chem. Soc. 119, 4021 (1997)], and it provides a useful way to describe the polarization effect in solution, with several advantages discussed in Sec. I. The s

The mass accommodation (condensation) coefficient α of water vapor into liquid water was theoretically studied via two complementary approaches: by molecular dynamics (MD) scattering simulation and by computational fluid dynamics simulation of the droplet train/flow reactor experiment. The MD scattering simulation predicts α ∼ 1 at 273 K. The fluid dynamics simulation quantitatively interprets the gaseous resistance in the droplet train flow tube, which demonstrated that the results of the dropl

The infrared-visible sum frequency generation (SFG) spectrum of the surface of water was calculated with significantly improved accuracy via the time-dependent formalism we have recently proposed. The revisions include molecular modeling of the OH stretching region, sampling statistics, and a treatment of boundary conditions. The calculated spectra show good agreement with recent experiments, allowing a detailed comparison and analysis.

The polarizability of a water molecule in liquid is evaluated via ab initio and density functional calculations for water clusters. This work has considerably improved our previous effort [J Chem Phys 1999, 110, 11987] to attain quantitative accuracy for polarizability. The calculations revealed that the water polarizability in the liquid is reduced from that in the gaseous phase by 7-9%. These results suggest significant implications for polarizable water models.

The effect of medium perturbation on the polarizabilities of solute molecules in condensed environment are evaluated and analyzed. Some solutes, including Ne, Ar, CH4, Cl−, and H2O, in liquid water and argon were treated employing a supermolecule approach with Monte Carlo simulations and ab initio molecular orbital calculations explicitly considering the solvent molecules. Dielectric solute–solvent interaction was calibrated to derive the intrinsic polarizabilities of solutes. The results reveal

Sum-frequency generation (SFG) spectra from charged solid–liquid interfaces include significant contribution from third-order susceptibility χ(3), which mainly originates from induced water orientation in the electric double layer. We quantitatively evaluate the χ(3) susceptibility by molecular dynamics simulation in aqueous electrolyte solutions with varying concentrations and temperatures. We found that the value of χ(3) decreases with increasing concentration or temperature and that the pertu

The mass accommodation coefficient α of the HO 2 radical in aqueous aerosols remains largely uncertain in atmospheric modeling. Therefore, in the present paper, a molecular dynamics computer simulation was performed to evaluate the HO 2 α in liquid water. The calculations yielded an α near unity, which defines a possible upper bound of the uptake coefficient γ. Implications for a large γ in the tropospheric atmosphere are discussed using model calculations for two typical cases: remote marine ai