The observed lines are from
(1) J. Gripp, A. Guarnieri, W. Stahl, and D. Lentz, 2000, J. Mol. Struct. 526, 81.
At low values of J and in cold sources the ¹⁴N hyperfine splitting may be resolvable. Therefore, a separate hyperfine calculation is provided.
Note: The partition function given below does not include ¹⁴N hyperfine splitting. The partition function values have to be multiplied with I(N) = 3 if hyperfine split transitions are considered !
The purely K-dependent parameters (A and D_K), needed to obtain reasonable intensities, were taken from CH₃NC;
(2) J. Plìva, L. D. Le, J. W. C. Johns, Z. Lu, and R. A. Bernheim, 1995, J. Mol. Spectrosc., 173, 423.
The dipole moment is from (1).
At low temperatures, it may be necessary to discern between A-CH₃CCNC and E-CH₃CCNC. The A states are described by K = 3n, the E states by K = 3n ± 1. The nuclear spin-weight ratio is 2 : 1 for A-CH₃CCNC with K>0 and all other states, respectively. The J_K = 1₁ state is the lowest E state. It is 5.3152 cm^–1 above ground.