On the improvement of the rotational structure analysis of¹³CH₃D ground vibrational state

The main goal of the present study was to improve the already published rotational structure analysis of the ground vibrational state of the¹³CH₃Dmolecule. To realise that,we recorded high-resolution spectra of a set of the strongly interacting vibrational bands, 2ν₃(A₁), 2ν₆(A₁), 2ν₆(E), ν₂(A₁), ν₅+ ν₆(A₁), ν₅+ ν₆(A₂), ν₅+ ν₆(E) and ν₃+ ν₆(E). From the analysis of the experimental data, more than 1900 ground state combination differences (GSCD) were determined with J^max= 18, ΔJ^max= 2 and K^max= 15. The a₁/a₂splittings of the states with quantum number K = 3 were taken into account. The presence of numerous forbidden transitions allowed us to determine with high accuracy GSCD not only with ΔK = 0, but with ΔK = ± 1, ± 2 and ± 3, as well. Spectroscopic parameters of the ground vibrational state were determined from the joint fit of the obtained GSCD (they are reproduced with d_rms= 0.00014 cm^-1). The 21 highly accurate THz-region transitions which were also used as input data, are reproduced with d_rms= 47 kHz.