Fourier transform infrared (FTIR) spectroscopy of formaldoxime (CH2NOH) in the 450–3800 cm−1 region and its [formula omitted] band

Abstract

The Fourier transform infrared (FTIR) spectrum of formaldoxime (CH2NOH) was recorded in the 700–3800 cm−1 region at the Australian Synchrotron with an unapodized resolution of 0.5 cm−1 to identify its fundamental and overtone bands and to measure their relative infrared (IR) intensities in this region. The high-resolution FTIR spectrum of the ν9 band of CH2NOH was also recorded with an unapodized resolution of 0.00096 cm−1 in the 450–600 cm−1 region for a rovibrational analysis. In the analysis of the A/B-hybrid type ν9 band, a total of 2011 infrared transitions (1655b-type and 356 a-type transitions) were fitted using the Watson's A-reduced and S-reduced Hamiltonians in the Ir representation with a root-mean-square (rms) deviation of 0.000096 cm−1 and 0.000305 cm−1 respectively. From this rovibrational analysis, the v9 = 1 state rotational constants (A, B and C) and five quartic terms (ΔJ, ΔJK, ΔK, δJ, δK) were improved from previous work and three sextic terms (ΦJK, ΦKJ, ΦK) were derived for the first time. The band center of the ν9 band of CH2NOH was found to be 530.0187764(63) cm−1 and 530.018762(18) cm−1 in the A-reduced and S-reduced Hamiltonians respectively. All five quartic and three sextic (ΦJK, ΦKJ, ΦK) centrifugal distortion terms of the ground state of CH2NOH were also improved with higher accuracy. They were obtained through the fitting of 3020 ground state combination differences (GSCDs) derived from the IR transitions of the ν9, ν12 and ν10 bands of CH2NOH, together with 23 previously reported microwave frequencies. The rms deviation of this GSCD fit was 0.000498 cm−1 and 0.000519 cm−1 in the A-reduced and S-reduced Hamiltonians respectively. Additionally, rotational constants and higher order centrifugal distortion terms of the ground and v9 = 1 states 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. The calculated and experimental rovibrational constants of CH2NOH for both ground and v9 = 1 states were in good agreement.