Methanethiol and its isotopologs undergo methyl internal rotation hindered by a moderately low barrier, similar to methanol and its isotopologs. In the case of CH₂DSH, this leads v_t = 0 to be split into three substates e₀ and o₁ of gauche-CH₂DSH and e₁ of anti-CH₂DSH. These substates are indicated by state numbers 0, 1, and 2, respectively. The linelist is based on an extensive analysis of microwave, sub-millimeter wave, terahertz, and FIR data pertaining to CH₂DSH in v_t = 0 presented in
(1) H. A. Bunn, S. Spezzano, L. H. Coudert, J.-C. Guillemin, Y. Lin, C. P. Endres, B. Billinghurst, O. Pirali, J. Jørgensen, V. Lattanzi, and P. Caselli, 2025, Astrophys. J. Lett. 980, Art. No. L13.
The line list includes previous microwave and lower millimeter data from
(2) C. F. Su and C. R. Quade, 1983, J. Chem. Phys. 79, 5828;
from
(3) C. F. Su, M. Liu, and C. R. Quade, 1993, J. Mol. Spectrosc. 158, 21;
and from
(4) C. R. Quade, M. Liu, and C. F. Su, 2007, J. Mol. Spectrosc. 244, 109.
The treatment of the data was described in some detail in (1); further details are available in (2-4) and additional articles cited in (1). Transitions in the fit extend to J = 24 and K = 12, which should be sufficient for astronomical observations. Unfortunately, no uncertainties were calculated for the transition frequencies, instead, a generic default of 0.5 MHz is given. More unfortunately, no line list has been provided thus far. It was stated in (1), that 3419 transition frequencies with microwave accuracy were fit to an rms of 0.27 MHz.
The dipole moment components and their first order torsional contributions were calculated from the dipole components of the main isotopic species taken from
(5) S. Tsunekawa, I. Taniguchi, A. Tambo, T. Nagai, T. Kojima, and K. Nakagawa, 1989, J. Mol. Spectrosc. 134, 63;
and from the derived CH₂DSH potential.
The quantum numbers in the catalog file are J, K, p, "v", where p = 1 or 2 is the parity, and "v" the state number of the torsional substate as specified above.
The partition function takes into consideration v_t = 0 with J and K extending to 32 and 12, respectively; g_I = 1 was applied. The partition function should be quite good up to temperatures of about 150 K; the most severe limitation at higher temperatures is the restriction to v_t = 0.