1. Millimeter-wave and high-resolution infrared spectroscopy of the low-lying vibrational states of pyridazine isotopologues.
- Author
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Esselman, Brian J., Zdanovskaia, Maria A., Amberger, Brent K., Shutter, Joshua D., Owen, Andrew N., Billinghurst, Brant E., Zhao, Jianbao, Kisiel, Zbigniew, Woods, R. Claude, and McMahon, Robert J.
- Subjects
INFRARED spectroscopy ,ISOTOPOLOGUES ,PYRIDAZINES ,COMPUTATIONAL chemistry ,EXCITED states ,SPECTRUM analysis ,VIBRATIONAL spectra - Abstract
The gas-phase rotational spectrum from 8 to 750 GHz and the high-resolution infrared (IR) spectrum of pyridazine (o-C
4 H4 N2 ) have been analyzed for the ground and four lowest-energy vibrationally excited states. A combined global fit of the rotational and IR data has been obtained using a sextic, centrifugally distorted-rotor Hamiltonian with Coriolis coupling between appropriate states. Coriolis coupling has been addressed in the two lowest-energy coupled dyads (ν16 , ν13 and ν24 , ν9 ). Utilizing the Coriolis coupling between the vibrational states of each dyad and the analysis of the IR spectrum for ν16 and ν9 , we have determined precise band origins for each of these fundamental states: ν16 (B1 ) = 361.213 292 7 (17) cm−1 , ν13 (A2 ) = 361.284 082 4 (17) cm−1 , ν24 (B2 ) = 618.969 096 (26) cm−1 , and ν9 (A1 ) = 664.723 378 4 (27) cm−1 . Notably, the energy separation in the ν16 -ν13 Coriolis-coupled dyad is one of the smallest spectroscopically measured energy separations between vibrational states: 2122.222 (72) MHz or 0.070 789 7 (24) cm−1 . Despite ν13 being IR inactive and ν24 having an impractically low-intensity IR intensity, the band origins of all four vibrational states were measured, showcasing the power of combining the data provided by millimeter-wave and high-resolution IR spectra. Additionally, the spectra of pyridazine-dx isotopologues generated for a previous semi-experimental equilibrium structure (re SE ) determination allowed us to analyze the two lowest-energy vibrational states of pyridazine for all nine pyridazine-dx isotopologues. Coriolis-coupling terms have been measured for analogous vibrational states across seven isotopologues, both enabling their comparison and providing a new benchmark for computational chemistry. [ABSTRACT FROM AUTHOR]- Published
- 2024
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