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A combined total of 25 vibrational states of 2-chloropyridine (C5H4NCl, la = 3.07 D, lb = 1.70 D), including states for both chlorine isotopologues, have been least-squares fit to sextic, A-reduced Hamiltonians with low error (<0.05 MHz). In total, over 22,500 transition frequencies were measured in the 135–375 GHz frequency region. The technique of fixing undeterminable distortion constants to the corresponding values of the ground vibrational state for fundamental states and to extrapolated values for overtone and combination states was employed. The experimentally determined rotational, centrifugal distortion, and vibration-rotation interaction constants are reasonably well-predicted by computational methods (B3LYP/6-311+G(2d,p)). For the chlorine isotopologues, the changes in rotational and quartic distortion constants upon vibrational excitation are quite similar, indicating that it is possible to estimate the constants of a lower-abundance isotopologue’s excited vibrational state using the change in constant observed in the higher-abundance isotopologue. The changes in rotational and quartic distortion constants upon vibrational excitation are also quite similar between analogous vibrational states of 2-chloropyridine and chloropyrazine, despite their differences in molecular composition.
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Vibrationally excited states of 1 H - and 2 H -1,2,3-triazole isotopologues analyzed by millimeter-wave and high-resolution infrared spectroscopy with approximate state-specific quartic distortion constants
In this work, we present the spectral analysis of 1 H- and 2 H-1,2,3-triazole vibrationally excited states alongside provisional and practical computational predictions of the excited-state quartic centrifugal distortion constants. The low-energy fundamental vibrational states of 1 H-1,2,3-triazole and five of its deuteriated isotopologues ([1- 2 H]-, [4- 2 H]-, [5- 2 H]-, [4,5- 2 H]-, and [1,4,5- 2 H]-1 H-1,2,3-triazole), as well as those of 2 H-1,2,3-triazole and five of its deuteriated isotopologues ([2- 2 H]-, [4- 2 H]-, [2,4- 2 H]-, [4,5- 2 H]-, and [2,4,5- 2 H]-2 H-1,2,3-triazole), are studied using millimeter-wave spectroscopy in the 130–375 GHz frequency region. The normal and [2- 2 H]-isotopologues of 2 H-1,2,3-triazole are also analyzed using high-resolution infrared spectroscopy, determining the precise energies of three of their low-energy fundamental states. The resulting spectroscopic constants for each of the vibrationally excited states are reported for the first time. Coupled-cluster vibration–rotation interaction constants are compared with each of their experimentally determined values, often showing agreement within 500 kHz. Newly available coupled-cluster predictions of the excited-state quartic centrifugal distortion constants based on fourth-order vibrational perturbation theory are benchmarked using a large number of the 1,2,3-triazole tautomer isotopologues and vibrationally excited states studied.
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- Award ID(s):
- 1954270
- PAR ID:
- 10433938
- Date Published:
- Journal Name:
- The Journal of Chemical Physics
- Volume:
- 158
- Issue:
- 4
- ISSN:
- 0021-9606
- Page Range / eLocation ID:
- 044301
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1063/5.0137340
