The entry is only a slightly modified version of the first one from Apr. 2002. The majority of the data from the millimeter and the lower submillimeter wave region were taken from
(1) M. Le Guennec, J. Demaison, G. Wlodarczak, and C. J. Marsden, 1993, J. Mol. Spectrosc. 160, 471.
The uncertainties chosen in the present calculation are 20 kHz (better than 50 kHz was stated). A very accurate J = 1 – 0 transition frequency was reported by
(2) C. D. Cogley, L. M. Tack, and S. G. Kukolich, 1982, J. Chem. Phys. 76, 5669. Additional longer wavelength data were taken from
(3) R. Trambarulo and W. Gordy, 1950, J. Chem. Phys. 18, 1613
and from
(4) L. F. Thomas, E. I. Sherrard, and J. Sheridan, 1955, Trans. Faraday Soc. 51, 619.
The purely K-dependent parameters A, D_K, and an estimate of H_K, needed to obtain reasonable intensities, were taken from the main isotopic species as described in
(5) H. S. P. Müller, S. Thorwirth, and F. Lewen, 2020, J. Mol. Struct. 1207, Art. No. 127769,
based on ground state combination loops from
(6) H. S. P. Müller, P. Pracna, and V.-M. Horneman, 2002, J. Mol. Spectrosc. 216, 397.
The calculations should be sufficient for all observational purposes. Some caution may be advised for transitions having high values of J and K.
At low temperatures, it may be necessary to discern between A-CH₃CCD and E-CH₃CCD. The A state levels are described by K = 3n, those of E state by K = 3n ± 1. The nuclear spin-weight ratio is 2 : 1 for A-CH₃CCD with K > 0 and all other states, respectively. The J_K = 1₁ level is the lowest E state level. It is 5.568 cm^–1 above ground.
The dipole moment was taken from
(7) J. S. Muenter, and V. W. Laurie, 1966, J. Chem. Phys., 45, 855.