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An approach for identifying resonances in vibrational perturbation theory calculations is introduced. This approach makes use of the corrections to the wave functions that are obtained from non-degenerate perturbation theory calculations to identify spaces of states that must be treated with degenerate perturbation theory. Pairs of states are considered to be in resonance if the magnitude of expansion coefficients in the corrections to the wave functions in the non-degenerate perturbation theory calculation is greater than a specified threshold, χ max . This approach is applied to calculations of the vibrational spectra of CH 4 , H 2 CO, HNO 3 , and cc-HOONO. The question of how the identified resonances depend on the value of χ max and how the choice of the resonance spaces affects the calculated vibrational spectrum is further explored for H 2 CO. The approach is also compared to the Martin test [J. M. L. Martin et al., J. Chem. Phys. 103, 2589–2602 (1995)] for calculations of the vibrational spectra of H 2 CO and cc-HOONO.
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Several levels of theory for description of isotope effects in ozone
We developed a multi-level theory for description of the intricate isotope effect in ozone. At 0th level of theory the role of molecular symmetry is taken into account. Although the important factors of 1/2 appear in seven different places in the formalism, this level of theory does not lead to any isotope effect. At the 1st level the effect of atomic masses is introduced to elucidate the roles of vibrational zero-point energies and rotational excitations. It is found that averaging over thermal distribution smooths isotopic differences and leads to a small net effect. At the 2nd level the process is assumed to proceed through independent diabatic ro-vibrational channels, which permits to determine contribution of shape resonances populated by tunneling. Resultant isotope effects do not look like experiment and the rate coefficient is too small. At the 3rd level the role of Feshbach resonances is determined, by accurate close-coupling calculations using hyper-spherical coordinates, adaptive grids, sequential diagonalization truncation technique and complex absorbing potential. Comparison with experiment is presented. Refs: J. Phys. Chem. A 122, 9177 (2018); J. Chem. Phys. 149, 164302 (2018).
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- Award ID(s):
- 1920523
- PAR ID:
- 10144018
- Date Published:
- Journal Name:
- 50th Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics APS Meeting
- Volume:
- 64
- Issue:
- 4
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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