Fourier transform infrared (FTIR) spectroscopy of formaldoxime isotopologue 12CD2NOH in the 300–3700 cm−1 region and its ν12 and ν9 bands: Vibrational and rovibrational analyses

The Fourier transform infrared (FTIR) spectrum of the formaldoxime isotopologue ¹²CD₂NOH was recorded in the 500–3700 cm⁻¹ region with a resolution of 0.50 cm⁻¹ to identify its fundamental, overtone and combination bands and to measure their relative infrared (IR) band intensities. Furthermore, the high-resolution (0.00096 cm⁻¹) FTIR spectrum of ${\nu }_{12}$ and ${\nu }_9$ bands of ¹²CD₂NOH was recorded in Australian Synchrotron in the 300–510 cm⁻¹ region for a rovibrational analysis. A total of 1060 IR transitions of the C-type ${\nu }_{12}$ band were fitted using the Watson's A-reduced Hamiltonian in the I^r representation with a root-mean-square (rms) deviation of 0.000524 cm⁻¹. From the rovibrational analysis, the $v_{12}$ = 1 state rovibrational constants up to all 5 quartic centrifugal distortion terms were derived for the first time. The band center of the ${\nu }_{12}$ band of ¹²CD₂NOH was found to be 391.214740(46) cm⁻¹. The ground state rovibrational constants up to all 5 quartic terms were determined for the first time by the fitting of 423 ground state combination differences (GSCDs) derived from the IR transitions of the ${\nu }_{12}$ band of ¹²CD₂NOH of this work. The rms deviation of the GSCD fit was 0.000473 cm⁻¹ using the Watson’s A-reduced Hamiltonian in the I^r representation. Furthermore, a total of 724 IR transitions of the predominantly B-type ${\nu }_9$ band of ¹²CD₂NOH were fitted with a rms deviation of 0.000360 cm⁻¹ to derive the band center at 465.151277(39) cm⁻¹ and rovibrational constants of the $v_9$ = 1 state up to 4 quartic terms for the first time. Additionally, all 3 rotational constants and 5 quartic centrifugal distortion terms of the ground state and 3 rotational constants of the $v_{12}$ = 1 and $v_9$ = 1 states of ¹²CD₂NOH were computed from theoretical anharmonic calculations at 2 different levels of theory, B3LYP and MP2 with the cc-pVTZ basis set, for comparison with the experimental results. Close agreement was found for the calculated and experimental rotational constants of ¹²CD₂NOH for the ground, $v_{12}$ = 1 and $v_9$ = 1 states. The vibrational frequencies (cm⁻¹) of 12 fundamental bands of ¹²CD₂NOH in the 300–3700 cm⁻¹ region, and their IR band intensities (km/mol) were also calculated using B3LYP and MP2 with the cc-pVTZ basis set, and they were compared with the respective experimental data.