Published papers

© 2018 Wiley Periodicals, Inc. One of the most spectacular yet unsolved problems for the ICN (Formula presented.) -band photodissociation is the non-statistical spin-rotation F1 = N + 1/2 and F2 = N − 1/2 populations for each rotation level N of the CN fragment. The F1/F2 population difference function f(N) exhibits strong N and λ dependences with an oscillatory behavior. Such details were found to critically depend on the number of open-channel product states, namely, whether both I (2P3/2) and I (2P1/2) are energetically available or not as the dissociation partner. First, in the asymptotic region, the exchange and dipole-quadrupole inter-fragment interactions were studied in detail. Then, as the diabatic basis, we took the appropriate symmetry adapted products of the electronic and rotational wavefunctions for the F1 and F2 levels at the dissociation limits. We found that the adiabatic Hamiltonian exhibits Rosen–Zener–Demkov type nonadiabatic transitions reflecting the switch between the exchange interaction and the small but finite spin-rotation interaction within CN at the asymptotic region. This non-crossing type nonadiabatic transition occurs with the probability 1/2, that is, at the diabatic limit through a sudden switch of the quantization axis for CN spin S from the dissociation axis to the CN rotation axis N. We have derived semiclassical formulae for f(N) and the orientation parameters with a two-state model including the 3A′ and 4A′ electronic states, and with a four-state model including the 3A′ through 6A′ electronic states. These two kinds of interfering models explain general features of the F1 and F2 level populations observed by Zare's grousp and Hall's group, respectively. © 2018 Wiley Periodicals, Inc.

Copyright © 2019 American Chemical Society. ICN is one of the few simple triatomic molecules whose photodissociation mechanisms have been thoroughly investigated. Since it has a linear structure in the electronic ground state, the dissociation follows a photoexcitation at a linear or slightly bent structure. It is generally believed that the Ã-band consists of the dominant excitation to 3 Π 0+ (4A′) with the transition dipole moment (TDM) parallel to the molecular axis (z), a slightly weaker transition to 1 Π 1 (5A′, 4A″), and a much weaker transition to 3 Π 1 (3A′, 2A″), both of the latter two having perpendicular TDMs. In the present work, we have theoretically studied the geometry dependence of these TDMs and found a pronounced θ (bending angle) dependence in the parallel (z) component of the TDMs to 1 Π 1 (5A′) and 3 Π 1 (3A′), both of which should be zero at a linear geometry by symmetry and thus have been previously ignored. We estimated that the z component TDM to 1 Π 1 (5A′) has a contribution of 15-20% to the total absorption cross-section at 249 nm at room temperature. Interestingly, the TDM to 3 Π 0+ (4A′) does not exhibit such θ dependency and thus has only the z component. We compare the TDMs of ICN and CH 3 I molecules having similar excited states. The fact that all the TDMs to 3A′, 4A′, and 5A′ have nonnegligible z components implies the importance of the coherent excitation contributions to various observables of CN fragment, such as the anisotropy parameter, the orientation parameter, and the rotational level distribution as well as the rotational fine structure level distribution.

The complex basis function (CBF) method is a square-integrable (L 2) function method that represents continuum wave functions, and has been applied successfully to various problems, including the calculation of resonance state energies and photoionization cross sections. The previous applications of this method have been limited to non-relativistic problems, and no serious attempt has been made for the relativistic Hamiltonian. In this study, we calculated the photoionization cross sections from the imaginary part of the frequency-dependent polarizability by applying the CBF method to the inhomogeneous Dirac equation of the one-electron uranium cation. The results obtained by employing a pure Coulomb potential to the K-shell photoionization cross sections were in good agreement with previous theoretical values and experimental values for the neutral uranium atom. Phase shifts were obtained by matching the CBF solutions with the numerical ones, which were further propagated by the fourth-order Runge–Kutta method, and thus, the photoionization differential and total cross sections were successfully calculated. The calculated results were analyzed from various viewpoints, including the multipole effect of electromagnetic fields, momentum conservation of photon and photoelectron, interference of multiple perturbation terms, and difference in the orbital angular momentum of the small component wave functions. These analyses demonstrate the effectiveness of the CBF method for the inhomogeneous Dirac equation and thus its applicability to multielectron systems.

The investigation of electron density migrations caused by molecular structure changes is of central importance in various fields of chemistry. To address this topic in general and to study absorption intensities of vibrations, we analyze sensitive dipole moment functions (DMFs) of a molecule by combining the linear response function of conceptual DFT and bond dipoles separated by the quantum theory of atoms in molecules with a graphical transition moment decomposition scheme. The fundamental intensities of OH stretching vibrations depend strongly on the substituents but only weakly on the molecular conformations. Interestingly, in some alcohols, completely opposite trends have been observed for the lower-level overtone intensities: a weak substituent dependence but a stronger conformation dependence. It is well known that the formation of a hydrogen-bonded complex increases the OH stretching fundamental intensity, but less well known is the decrease in their overtone intensities. To investigate these characteristics comprehensively, we calculated their intensities (Δv = 1, 2, and 3) for conformers of ethanol and trifluoroethanol (TFE) and hydrogen-bonded phenol (PhOH) systems via the DFT method in the local mode model for the OH stretching coordinate ΔR. Their first and second derivatives of the electron density with respect to ΔR were calculated and interpreted using their bond moments. For ethanol and TFE, the OH, CC, and CH bond moments were found to make an important contribution to the molecular DMF derivatives parallel to the OH bond. The OH bond contributes only to the first derivative of DMF, and its conformational dependence is determined by the magnitude of the charge polarization of each structure. The electron density derivatives in the CC bond region were largely maintained during the internal rotation; thus, their conformation-dependent contributions were expressed by a geometrical factor of the CC bond direction. The CH bond at the antiperiplanar position of the OH bond was found to make a remarkably large contribution to the second derivative of DMF in the gauche conformer. The importance of electron density migration on substituents was also identified in the hydrogen-bonded phenol, in which the π-electron density change on the aromatic ring was clearly shown. This migration creates the DMF derivatives both perpendicular and parallel to the OH bond and strongly affects the absorption intensities. In all the cases, some bond moments on the substituents contribute to the first and second DMF derivatives in a structure-dependent manner, thus explaining their stereoelectronic effects.

Polyynes (C2nH2) show the unusually strong πg + πu combination bands in the infrared absorption spectra. We calculated them as the first overtone of the local CCH bending; the strong intensities are interpreted as a consequence of the large-amplitude bending vibration of the acidic acetylenic hydrogen combined with the size-dependent πelectron conjugation. Our theoretical calculations show that the absorption intensity increases steadily and their increase rate is gradually slowed down by increasing the number of acetylene units up to n = 9. However, the calculated vibrational wavenumber converges quickly in agreement with the experimental observation. The second-order electron density deformation caused by the local CCH bending was analyzed using the linear response functions, including the linear and nonlinear contributions, to explain the n dependence. The easily polarizable πelectron density caused two kinds of deformation - dominant but dark δxx-yy type and minor but bright σ type. Both of them exhibit interesting zigzag sign alternations, consistent with the law of alternating polarity of Coulson and Longuet-Higgins. The electron density polarization in these intra- and interacetylene units induces a large axial component molecular dipole moment, contributing to the intensity that increases with n. The difference between the curvilinear and rectilinear bending coordinates is interpreted within the present theoretical scheme.

Various minimum energy geometries, transition state geometries and possible reaction pathways have been investigated at the ab initio level of theories for the atmospheric important reaction between IO and BrO radicals. We employed SDB (Stuttgert-Dresden-Bonn)-cc-pVTZ basis sets for bromine and iodine and cc-pVTZ basis set for oxygen augmented with a set of diffuse functions (s,p) for each atom. The geometries and energetics have been studied at the MP2 and QCISD(T)//MP2 levels of theory, respectively. Possible reaction pathways for different product channels have been discussed on the basis of structural information and energetics along with results of the IRC calculations.