Dimethylacetylene: the theory required to analyse the infrared and Raman perpendicular bands Original Research Article

In this paper we give a detailed account of the theory required to simulate and analyse the infrared and Raman perpendicular fundamental bands of the dimethylacetylene molecule at high resolution. A summary of this theory has appeared in a previous paper (P.R. Bunker, J.W.C. Johns, A.R.W. McKellar and C. di Lauro, J. Mol. Spectry. 162 (1993) 142) in which an analysis of the infrared methyl rocking fundamental band was given. As well as detailing the effect of various terms in the Hamiltonian we also discuss the Raman selection rules and show that the analysis of the ΔK = 2 component of the perpendicular fundamental bands will lead to a determination of the sign of the torsional barrier. The sign of the barrier (i.e. whether the minimum energy conformation is staggered or eclipsed) cannot be determined from the analysis of the infrared perpendicular bands.