Vibrational bands of formaldoxime isotopologue 13CD2NOH in the 280–4000 cm−1 region and rovibrational analysis of its ν12 band by Fourier transform infrared (FTIR) spectroscopy

Abstract

A total of 11 fundamental and 3 overtone bands of the formaldoxime isotopologue ¹³CD₂NOH were identified using its Fourier transform infrared (FTIR) spectra which were recorded with a low resolution (0.50 cm⁻¹) in the 500–4000 cm⁻¹ region, and high resolution (0.00096 cm⁻¹) in the 280–500 cm⁻¹ region. Their relative infrared (IR) band intensities were also measured. Furthermore, a rovibrational analysis of the IR transitions of the ${\nu }_{12}$ band of ¹³CD₂NOH was carried out using its high-resolution FTIR spectrum which was recorded at the Australian Synchrotron. A total of 1077 IR transitions of the C-type ${\nu }_{12}$ band were assigned and fitted using the Watson's A-reduced Hamiltonian in the I^r representation to derive its band center and the $v_{12}$ = 1 state rovibrational constants up to all 5 quartic centrifugal distortion terms for the first time, with a root-mean-square (rms) deviation of 0.00044 cm⁻¹. The band center of the ${\nu }_{12}$ band of ¹³CD₂NOH were found to be 391.054446(36) cm⁻¹. The ground state rovibrational constants up to all 5 quartic terms were determined for the first time by fitting 407 ground state combination differences (GSCDs) derived from the assigned IR transitions of the ${\nu }_{12}$ band of ¹³CD₂NOH of this work. The rms deviation of the GSCD fit was 0.00040 cm⁻¹. Additionally, all 3 rotational constants and 5 quartic centrifugal distortion terms of the ground state and 3 rotational constants of the $v_{12}$ = 1 state of ¹³CD₂NOH were computed from theoretical anharmonic calculations at two 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 rovibrational constants of ¹³CD₂NOH for both ground and $v_{12}$ = 1 states. The vibrational anharmonic frequencies of the 12 fundamental bands of ¹³CD₂NOH in the 280–4000 cm⁻¹ region, and their IR band intensities were also calculated using B3LYP and MP2 with the cc-pVTZ basis set, and they were compared with the respective experimental data. Finally, the ground state rotational constants and the band center of the ${\nu }_{12}$ band of the cis conformer of ¹³CD₂NOH were calculated and compared with those of the trans conformer of this work.