Approximate Selection Rules for |K| = 1-0 and 1-1 Tunneling-Rotation Transitions in the Methanol Dimer

Approximate K = 0 and |K| = 1 tunneling-rotation eigenfunctions for the four A, four E, and one G symmetry species present in the methanol dimer, derived from molecular parameters obtained previously from a least-squares fit to transition frequencies involving K = 0 and 1 levels, are used to clarify some apparent contradictions associated with traditional b- and c-type transition designations in the E and G tunneling-rotational states of this dimer. These approximate eigenfunctions also predict strong and weak line intensities which are consistent with the pattern of strong a-, b-, and c-type transitions observed, thus supporting our previous separate K-state analysis based only on energy level differences. Some of the predicted weaker |K| = 1 a-type transitions should be experimentally observable with more signal averaging. Copyright 2000 Academic Press.