CDMS

The v₁₀ = 1 state of propyne is the lowest excited, doubly degenerate bending state of this molecule. It corresponds to v₈ = 1 of CH₃CN, which has been detected in the ISM. The rotational lines were taken from
(1) A. Bauer and J. Burie, 1969, C. R. Acad. Sci. Paris, Ser. B 268, 800;
(2) J. M. Ware and J. A. Roberts, 1984, J. Chem. Phys. 81, 1215;
(3) G. Wlodarczak, R. Bocquet, A. Bauer, and J. Demaison, 1988, J. Mol. Spectrosc. 129, 371; and
(4) H. S. P. Müller, P. Pracna, and V.-M. Horneman, 2002, J. Mol. Spectrosc. 216, 397.
Transitions with the state number 1 and 2 are those with K·l₁₀ ≤ 0 and > 0, respectively.
The data have been subjected to a combined fit with the ν₁₀ band data from (4), the v = 0 data from (4) and references therein (see also e040502.cat). The interactions of v₁₀ = 1 with v₉ = 1 and v₁₀ = 2, as described in (4), have been taken into account. In particular because of these interactions, predictions with k ≡ K·l₁₀ < –11 should be viewed with some caution.
The dipole moment is assumed to be the same as for the v = 0 state, e040502.cat.
The nuclear spin-weight ratio is 2 : 1 for A-CH₃CCH with k + l₁₀ > 0 and all other states, respectively. The A state levels are described by k = 3n + l₁₀, those of E state by k = 3n + l₁₀ ± 1.
Besides the ground vibrational state, the partition function takes into account the states v₁₀ = 1, v₉ = 1, and v₁₀ = 2. Their respective contributions are given in parentheses as long as they are different from 0 within the quoted digits.