Frequency Shifts and Noncoincidence Effect of the CN Stretching Modes and the Solvation Structures of Acetonitrile Electrolyte Solutions Miyu Hirose, Yukichi Kitamura, Hideaki Shirota, Hajime Torii Journal of Physical Chemistry B, 2025 Electrolyte solutions often show characteristic spectral features in their vibrational spectra, and a quantitative analysis of them is a key toward better understanding of the solvation structures and intermolecular interactions based on those spectral features. Here, such an analysis is carried out for the C≡N stretching mode of some electrolyte solutions of acetonitrile. It is found that a negative noncoincidence effect, in which the isotropic Raman component is located at a higher frequency than the anisotropic component, is observed for the band that newly appears upon solvation of salt, and based on a theoretical analysis that refers to quantum chemical calculations and molecular dynamics simulation results, it is shown that this phenomenon arises from the vibrational coupling among the C≡N bonds clustering around each metal ion (Li+, Mg2+, Ca2+, or Zn2+). The transition dipole coupling mechanism reasonably well explains the sign and magnitude of this intermolecular vibrational coupling. The overall high-frequency shift of this newly appearing band (compared to the band of neat liquid) is largely explained by an electrostatic interaction model that takes into account the spatially nonuniform nature of the electrostatic potentials and fields operating from each metal ion on the solvent molecules around it. On the basis of these results, the relation between the spectral features and the solvation structures is discussed.
Single-Sided Delocalized Polarization of the C60 Cage and Reduced Infrared Intensities and Dipole Moment of H2O@C60 Hajime Torii, Shumpei Sadai, Yoshifumi Hashikawa, Yasujiro Murata, Yuka Ikemoto Journal of Physical Chemistry A, 2024 The C60 fullerene cage can encapsulate a small molecule like water and provides room to leave the encapsulated component rather isolated, but the true nature of the intracomplex interactions should be further elucidated for better understanding and utility of this series of complexes. Here, an analysis toward this goal is conducted for H2O@C60 by infrared spectral measurements and theoretical calculations. It is shown that the response of the π electrons of the C60 cage upon encapsulating a water molecule is single-sided and delocalized in that the electron density is partially transferred from the −z side to the +z side of the cage (when the z axis is taken along the water dipole) but almost only inside the cage, explaining the significant reduction of the dipole moment and the infrared intensities. Those infrared intensities have a large temperature dependence in a way that the bands gain intensities upon lowering the temperature down to 10 K, possibly due to coupling with lattice phonons.
Modeling of the Hydrogen Bond-Induced Frequency Shifts of the HOH and HOD Bending Modes of Water Hajime Torii, Tomoka Akazawa Journal of Physical Chemistry A, 2024 The intramolecular bending mode of water is a possible useful probe of the hydrogen-bond situations in aqueous systems, but the behavior of its frequency and intensity should be further elucidated for better understanding on its nature and, hence, for its better utilization as a probe. Here, an analysis toward this goal is conducted by doing theoretical calculations on molecular clusters of normal isotopic and deuterated species of water and examining the correlations among the vibrational, structural, and electrostatic properties. It is shown that electrostatic interactions, particularly both of the in-plane components of the electric field along the OH bond and perpendicular to it, play a major role in controlling the hydrogen bond-induced shifts of the force constant, but additional factors, including the intermolecular structural and/or charge-transfer properties, are also important. Models of the hydrogen bond-induced shifts of the force constant are presented in a form that may be combined with classical molecular dynamics. With regard to the infrared intensity changes, it is shown on the basis of the electron density analysis that the intermolecular charge flux and polarization effect play an important role, depending on the angular characteristics of the hydrogen bond.
Roles of electrostatics and intermolecular electronic motions in the structural and spectroscopic features of hydrogen- and halogen-bonded systems Hajime Torii Pure and Applied Chemistry, 2024 It is widely recognized that electrostatics plays a central role in the intermolecular interactions in condensed phases, as evidenced by the “electrostatics + Lennard-Jones” form of the potential functions that are commonly used in classical molecular dynamics simulations. Then, do we understand all about electrostatics in condensed phases? In this review, recent theoretical advances in relation to this topic will be discussed: (1) vibrational spectroscopic probing of the electrostatics in condensed phases, and (2) some phenomena affected by deviation from the scheme of isotropic fixed atomic partial charges, i.e., anisotropy and intermolecular transfer of electron distributions. A theoretical basis for better understanding on them and some theoretical models for practical calculations will be shown with some typical example cases of hydrogen- and halogen-bonded systems.
Asymmetry of the Electrostatic Environment as the Origin of the Symmetry Breaking Effect of the Nitrate Ion in Aqueous Solution Hajime Torii, Kao Watanabe Journal of Physical Chemistry B, 2023 Elucidating the mechanism of how vibrational modes are affected by intermolecular interactions is important for a better understanding of the nature of the former as probes of the latter. Here, such an analysis is carried out for the N-O stretching modes of the nitrate ion interacting with water, with an emphasis on the symmetry breaking effect. On the basis of theoretical calculations on the structural, vibrational, and electrostatic properties of molecular clusters and spectral simulations for an aqueous solution, a transparent view is demonstrated on the mechanism that modulations of spatially local electrostatic environment give rise to structural and spectroscopic symmetry breaking effect. The electrostatic interaction model constructed here is a seven-parameter model; the use of a single electrostatic parameter, such as the electric field on a single atomic site, is found to be insufficient for quantitative evaluation. It is also shown that the frequency modulations of the N-O stretching modes in aqueous solution occur on a time scale much shorter than 0.1 ps.
Substituent Effect and Its Halogen-Atom Dependence of Halogen Bonding Viewed through Electron Density Changes Takanori Sakai, Hajime Torii Chemistry an Asian Journal, 2023 Elucidating how the halogen‐bonding ability and strength are controlled by the substituent effect and how this control depends on halogen atom will be essential for finely‐tuned design of functionally important molecules. Here, this problem is tackled by analyzing the electron density differences/changes for variously substituted halobenzenes. It is shown that the anisotropy of the electron distribution around the halogen atom, which is an important factor for halogen‐bonding ability, is not much affected by the substituent effect and rather simply depends on the halogen atom, while the partial charge on the halogen atom, which is related to the bond dipole of the C−X bond, is significantly modulated by the substituent effect and gives rise to enhancement of the electrostatic potential on the line extended from the C−X bond. The properties related to the polarization effect are also discussed.
What electron densities and their changes tell us about intermolecular interactions Hajime Torii Aip Conference Proceedings, 2022 Features of the electron densities and their changes induced by intermolecular interactions are examined, in relation to the structural and/or vibrational properties, for hydrogen- and halogen-bonding systems by taking two specific cases. It is shown that analyses of electron densities and their changes provide us decisive information that is helpful to deepen our understanding on intermolecular interactions.
Theoretical analysis toward better description of the wavenumber shifts of the OH stretch of hydrogen-bonded water Yukichi Kitamura, Hajime Torii Journal of Raman Spectroscopy, 2022 Relating vibrational properties to intermolecular configurations is generally important for correct analysis and interpretation of infrared and Raman spectra of condensed‐phase systems. Here, a theoretical analysis in this direction is conducted through calculations on (water)90 clusters for better description of the OH stretch of hydrogen‐bonded water. It is shown that, while the electric field descriptor related to the vibrating OH bond primarily describes the wavenumber shift arising from hydrogen‐bond formation, the secondary descriptors related to the other OH bond in the same water molecule noticeably improve the performance of theoretical modeling. It is also shown that, for the electric field descriptor, the electric charge configuration is an important factor for good performance. Explicit forms of those descriptors are presented that may be applicable to spectral simulations through combination with classical molecular dynamics. The mechanism behind the secondary descriptors is also discussed.
Vibrational Spectroscopic Map, Vibrational Spectroscopy, and Intermolecular Interaction Carlos R. Baiz, Bartosz Błasiak, Jens Bredenbeck, Minhaeng Cho, Jun-Ho Choi, Steven A. Corcelli, Arend G. Dijkstra, Chi-Jui Feng, Sean Garrett-Roe, Nien-Hui Ge, Magnus W. D. Hanson-Heine, Jonathan D. Hirst, Thomas L. C. Jansen, Kijeong Kwac, Kevin J. Kubarych, Casey H. Londergan, Hiroaki Maekawa, Mike Reppert, Shinji Saito, Santanu Roy, James L. Skinner, Gerhard Stock, John E. Straub, Megan C. Thielges, Keisuke Tominaga, Andrei Tokmakoff, Hajime Torii, Lu Wang, Lauren J. Webb, Martin T. Zanni Chemical Reviews, 2020
Intensity-carrying vibrational modes important for nonlinear optical properties derived from algebraic properties of intensity formulas Molecular Crystals and Liquid Crystals Science and Technology Section B Nonlinear Optics, 2000
Low-Wavenumber Vibrational Dynamics of Liquid Formamide and N-Methylformamide: Molecular Dynamics and Instantaneous Normal Mode Analysis Journal of Physical Chemistry A, 2000
