High resolution infrared spectra of ethane-like molecules and the barrier to internal rotation: Structure of the perpendicular bands of dimethylacetylene

Abstract

The fine structure of the perpendicular bands of an ethane-like molecule with nearly free internal rotation is discussed from the point of view of determining the barrier to internal rotation. The existing theory is extended to take into account the variation of the rotational constants with vibrational state, the ( P x p x + P y p y )-Coriolis coupling between the fundamental levels of the degenerate generate and nondegenerate CH stretching vibrations, and the Fermi resonance between the fundamental levels of the CH bending vibration. The structure of several “hot” bands associated with the low frequency skeletal bending vibrations is also discussed.