Improved ground state and [formula omitted] = 1 state rovibrational constants of formaldoxime (CH2NOH)

Abstract

The high-resolution Fourier transform infrared (FTIR) spectrum of the ν12 band of formaldoxime (CH2NOH) was recorded at the Australian Synchrotron with an unapodized resolution of 0.0018 cm−1 in the 320–460 cm−1 region. A total of 1895 infrared transitions were fitted using the Watson's A-reduced Hamiltonian in the Ir representation with a root-mean-square (rms) deviation of 0.000156 cm−1. From this rovibrational analysis, the ν12 = 1 state rotational constants (A 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 ν12 band of CH2NOH was found to be 397.685235(23) cm−1. All five quartic centrifugal distortion terms of the ground state were also improved with higher accuracy. The ground state ΦJK, ΦKJ, ΦK were obtained for the first time through the fitting of 1501 ground state combination differences (GSCDs) derived from the IR transitions of the ν12 and ν10 bands, together with 23 previously reported microwave frequencies. The rms deviation of this GSCD fit was 0.000687 cm−1. Additionally, rotational constants and higher order centrifugal distortion terms of the ground and v12 = 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 v12 = 1 states were in good agreement.