The transition frequencies 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 30 kHz (better than 50 kHz was stated). 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
(2) H. S. P. Müller, S. Thorwirth, and F. Lewen, 2020, J. Mol. Struct. 1207, Art. No. 127769,
based on ground state combination loops from
(3) 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-CH₃¹³CCD and E-CH₃¹³CCD. 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-CH₃¹³CCD 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 assumed to agree with that of CH₃CCD, which was taken from
(4) J. S. Muenter, and V. W. Laurie, 1966, J. Chem. Phys., 45, 855.