Vibration—rotation bands of deuteromethyl acetylene CH 3CCD

Abstract

Vibration—rotation bands of methyl acetylene- d 1 have been analysed. Structure has been resolved in five parallel bands (ν 1, ν 2, ν 3, 2ν 9 and 2ν 8) and values have been derived for a number of the coefficients α A and α B relating the rotational constants A and B in different vibrational states. The perpendicular bands associated with four fundamental degenerate vibrations have been measured. For ν 6 and ν 8 the Q branches have been analysed and fitted to expressions from which [ A′ (1 − ζ) − B′] and (α A − α B ) have been determined. The band ν 7 is perturbed by both Coriolis interaction and Fermi resonance, but an analysis has been made. The Coriolis perturbation between ν 7 and ν 4, and Fermi resonance between ν 7 and (ν 8 + ν 10) have been interpreted. An unusual structure has been observed with the band ν 9 arising from the particular value of ζ and the relative values of the rotational constants A and B. Using all the data, the sum rule, and the value of A 0 previously found for methyl acetylene, values have been determined for ζ 6 = 0·07 5, ζ 7 = −0·33, ζ 8 = 0·38 9, ζ 9 = 0·99 5, and ζ 10 = 0·89 7.