Data involving v_t ≤ 2 were subjected to a combined fit. The experimental data were summarized by
(1) V. V. Ilyushin, C. P. Endres, and F. Lewen, S. Schlemmer, and B. J. Drouin, 2013, J. Mol. Spectrosc. 290, 31.
The majority of the (mostly) submillimeter data are from that work. They were supplemented by additional data from
(2) V. V. Ilyushin, E. A. Alekseev, S. F. Dyubko, and I. Kleiner, 2003, J. Mol. Spectrosc. 220, 170;
from
(3) V. V. Ilyushin, E. A. Alekseev, S. F. Dyubko, S. V. Podnos, I. Kleiner, L. Margulès, G. Wlodarczak, J. Demaison, J. Cosleou, B. Mate, E. N. Karyakin, G. Yu. Golubiatnikov, G. T. Fraser, R. D. Suenram, and J. T. Hougen, 2001, J. Mol. Spectrosc. 205, 286;
from
(4) B. P. van Eijck and F. B. van Duijneveldt, 1983, J. Mol. Spectrosc. 102, 273;
from
(5) J. Demaison, A. Dubrulle, D. Boucher, J. Burie, and B. P. van Eijck, 1982, J. Mol. Spectrosc. 94, 211;
from
(6) G. Wlodarczak and J. Demaison, 1988, Astron. Astrophys. 192, 313;
from
(7) B. P. van Eijck, J. van Opheusden, M. M. M. van Schaik, E. van Zoeren, 1981, J. Mol. Spectrosc. 86, 465;
and from
(8) L. C. Krisher and E. Saegebarth, 1971, J. Chem. Phys. 54, 4553.
The majority of the data within v_t = 0 are from (1). Additional data are from (3), (5), (6), (7), and (8). The calculations should be reliable throughout because of the very large quantum number coverage and because of limiting the calculations to transition frequencies with calculated uncertainties below 0.1 MHz.
Please note: the fifth quantum number is not a standard quantum number. It designated the symmetry of the methyl internal rotor: 0 is E, 1 is A1, 2 is A2.
The partition function takes into account torsional states up to v_t = 8.
The ground state dipole moment components were determined in (8).