The entry is based on
(1) H. S. P. Müller, V. V. Ilyushin, A. Belloche, F. Lewen, and S. Schlemmer, 2024, Astron. Astrophys. 688, Art. No. A201.
The study combines rotational and rovibrational data pertaining to v_t = 0 and 1 plus some low energy K transitions of v_t = 2. By far the most data are from this work. A small amount of transitions in v_t = 0 below 36 GHz are from
(2) Y. Hoshino, M. Ohishi, and K. Takagi, 1991, J. Mol. Spectrosc. 148, 506.
Also used in the fit were far-infrared transition frequencies from
(3) G. Moruzzi, R. J. Murphy, J. Vos, R. M. Lees, A. Predoi-Cross, and B. E. Billingurst, 1991, J. Mol. Spectrosc. 268, 211.
A small number of transitions between the lowest two torsional states gain intensity through torsion-rotation interaction. Some of these lines were recorded in the laboratory. The entry provides ¹⁷O hyperfine splitting throughout, even though most of the lines are probably not resolved in astronomical spectra. However, many of the particularly important low energy transitions may be resolved.
The quantum numbers are J, K_a, K_c, m, and F. The values 0 and 1 of m correspond to A and E symmetry levels, respectively, of v_t = 0, and the values -3 and -2 correspond to A and E symmetry levels, respectively, of v_t = 1. The sign of K_a (with "+" omitted") reflects the parity for A symmetry states and the usual signs of K values in degenerate vibrational states for E symmetry states.
The calculated frequencies should be reliable throughout; some caution is advised for transitions reaching the limit of J (50) or K_a (17).
Please note: No experimental lines have been merged in the present entry. The list of experimental lines (with reference labels) can be accessed in the Cologne Spectroscopy Data section. The rotation-torsional part of the partition function is converged. Very small contributions by small amplitude vibrations have been omitted. Please note the mostly non-standard temperatures. These were evaluated by replacing g_N with g_F and with g_I = 1; the line strength of an unresolved line was distributed over the hyperfine components.
The dipole moment components are averages from measurements of CH₃¹⁶OH by
(4) I. Mukhopadhyay and K. V. L. N. Sastry, 2015, J. Mol. Spectrosc. 312, 51;
and of CH₃¹⁸OH by
(5) K. V. L. N. Sastry, I. Mukhopadhyay, P. K. Gupta, and J. VanderLinde, 1996, J. Mol. Spectrosc. 116, 38;
the remainder of the dipole moment function was taken from
(6) M. A. Mekhtiev, P. D. Godfrey, and J. T.Hougen, 2021, Infrared Phys. Technol. 116, Art. No. 103605.