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Accurate ab initio theoretical studies of rovibronic states of some simple diatomic molecules
Accurate ab initio theoretical studies of rovibronic states of some simple diatomic molecules
岡田, 一俊
7778
オカダ, カズトシ
7779
OKADA, Kazutoshi
7780
総合研究大学院大学
博士（理学）
Fundamental diatomic molecules and their rovibronic and tonic states have been paid an interest both experimentally and theoretically for so many years. Experimentally, there have been so many rotationally resolved absorption and emission spectra of diatomic molecule using grating, laser and so on. There have also been many spectra for the ionic states using photoelectron light source, and recent development in the photoelectron spectroscopy such as ZEKE, or PFI-PE, rotationally resolved spectra have been observed for those ionic states. There are also many theoretical studies using ab initio molecular orbital method. Fundamental diatomic molecules and their electronic excited states have been studied by using the configuration interaction method for a few decades. Recent development of molecular orbital theory and fast computer has made it possible to calculate the vibrational and rotational levels as well as electronic states more accurately. It is now possible to reproduce experimental data and the agreement between experimental data and theoretical results is very excellent and quantitative comparison of other properties is also possible. Theoretical calculations can also give very good prediction to for the states with no experimental data available. As both experiments and calculations become more accurate, calculated results with less accuracy become insufficient, and more accurate calculations are expected, but there are still few accurate calculation enough to explain experimental data quantitatively. In the present theoretical studies, accurate calculations were performed for several diatomic molecules and their ion, and their rovibrational levels.
In their accurate calculations, very large basis set, such as augmented quadruple zeta basis set, is used. Multireference configuration interaction (MRCI) calculations were performed for several electronic states of diatomic molecule. To describe properly the anti-bonding nature of molecular orbitals, valence-type-vacant(VALVAC) orbital method is used. The method requires only a single Fock matrix generation, and provides them with a proper anti-bonding nature of molecular orbitals. These orbitals are used as a reference space in the MRCI. In this method, they do not need to solve the state-averaged MCSCF. With a single set of molecular orbitals obtained by VALVAC method, the accurate potential energy and dipole moment functions both for the ground state and for the<br />excited states are obtained. All the calculated results are compared with recent experimental data, which are in excellent agreement.
The topics and their summaries of the results are as follows.
(1) Accurate potential energy and transition dipole moment curves for several electronic states of CO+.
Ab initio MO studies are performed for several doublet and quartet states of CO+ using the multi-reference Configuration interaction method. The neutral ground state of CO is also calculated. The following properties are compared with available experimental data.
(i) Low-lying electronic states, their rovibrational levels of each state up to the dissociation limit, and spectroscopic constants.
Adiabatic potential energy curves of several doublet and quartet states are calculated, and the vibrational levels are calculated using the potential energy curves. Spectroscopic constants, such as Re, ωe and ωexe are obtained. For example, for the X2Σ+ state, the calculated Re, ωe and ωexe are 1.1151 Å, 2214.6 cm-1, and 14.75 cm-1. Corresponding recent experimental values of Re, ωe and ωexe are 1.119 Å, 2215.1 cm-1, and 15.27 cm-1. Calculated spectroscopic constants well reproduce the recent experimental data.
(ii) ν dependence of rotational constant Bv.
The rotational constant Bv is obtained for each vibrational level. Rotational constants such as Be, and αe are calculated. The calculated Be and αe are 1.981 cm-1, and 0.0234 cm-1. Corresponding experimental values are 1.9798 cm-1 and 0.0202 cm-1. Calculated rotational spectroscopic constants also well reproduce experimental data.
(iii) The transition dipole moment functions and the lifetimes of the vibrational levels.
Transition dipole moment functions between the electronic states are also calculated. The lifetimes of the vibrational levels are evaluated by obtaining the Einstein's A coefficients, and the lifetimes are compared with experimental data. Calculated lifetime of the vibrational level ν=0 of the B2Σ+ state of CO+ is 56.40 ns. Corresponding experimental value is 57.1 ns. This agreement implies that the calculated Einstein's A coefficients to the lower electronic state are accurate.
(2) Ab initio studies of several excited states of CO+.
The adiabatic potential energy curves of the X2Σ+, A2II, B2Σ+, C2Δ, D(2)2II and 32II states of CO+ are calculated, and the vibrational levels of each state and spectroscopic constants are obtained. The vibrational levels of the D(2)2II and 3 2II states are particularly focused on. Adiabatic potential energy curves of the D(2)2II state shows that there is an avoided crossing between the D(2)2II and the 3 2II states. The splitting is about 1200 cm-1. Calculated vibrational levels using adiabatic potential energy curve show that here are only 3 vibrational levels. However, experimental data shows a vibrational progression of the D(2)2II state; the progression reaches up to ν=9. Experimentally obtained ν=9 level lies well above the barrier of the adiabatic potential energy curve or the D(2)2II and the 3 2II state, too. Thus, it the experimental assignment to the vibrational progression is correct, the vibrational levels above ν=2 have to be on the diabatic potential energy curve. The experimental data shows that the diabatic represention of the states is a good approximation to describe the rovibrational levels. To confirm it, the spectral intensities and their bandwidths of the vibrational levels on the diabatic potential energy curve are calculated and compared with experimental data.
(3) Accurate potential energy and transition dipole moment curves for several electronic states of N2+.
Ab initio MO studies are performed for several doublet and quartet states of N2+ using the multireference configuration interaction method. The following properties are compared with available experimental data. Spectroscopic constants, such as Re, ωe and ωexe are obtained. For the X2Σg+ state, the calculated Re, ωe and ωexe are 1.119 Å, 2212.3 cm-1, Blld 16.87 cm-1. Corresponding recent experimental values of Re, ωe and ωexe are 1.11642 Å, 2207.0 cm-1, and 16.10 cm-1. Also in this case, the agreement between the calculated results and experimental data is excellent.
(3) Rovibrational studies the neutral CO and investigations of rotational temperature of CO in the sun.
Rovibrational levels and their spectral intensities for absorption up to ν=9 and J=150 are calculated for the X1Σ+ state of CO. Calculated spectral intensities are compared with experimental data observed from the sun by satellite. A few different rotational temperatures are assumed to calculate the spectra, because the spectral intensities depend on rotational temperature. Calculated spectral intensities are compared with experimental data. Using the calculated result with known rotational temperature, rotational temperature of CO in the sun is estimated to be about 5000 K.
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総研大甲第446号
thesis
2000-03-24
AM
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https://ir.soken.ac.jp/record/201/files/甲446_要旨.pdf
https://ir.soken.ac.jp/record/201/files/甲446_本文.pdf
https://ir.soken.ac.jp/records/201
eng