ANALYSIS AND GLOBAL FIT OF TUNNELING SPLITTINGS IN THE K=0 A-TYPE MICROWAVE-SPECTRUM OF THE METHANOL DIMER

Theoretical results previously developed using an internal-axis-method -like multidimensional tunneling formalism are applied to recently mea sured tunneling splitting patterns for a-type R(J) microwave transitio ns in 10 different isotopomers of the methanol dimer. Permutation-inve rsion group G(36) species assignments for the 16 tunneling components of a given R(J) transition (split by 25 different tunneling motions) a re presented for 0 less than or equal to J less than or equal to 4 for the normal isotopomer. Permutation-inversion group G(18) species assi gnments for the 10 tunneling components of a given R(J) transition (sp lit by 13 different tunneling motions) are presented for 0 less than o r equal to J less than or equal to 3 for the two mixed C-12, C-13 isot opomers. As a first stage of the analysis, a simplified two-top treatm ent of suitably averaged measured line frequencies is carried out in w hich only the(dominant) tunneling splittings arising from internal rot ation of the two methyl tops of the dimer are considered. Relatively l arge top-top interaction terms must be included in this two-top treatm ent, which is surprising in view of the large distance between the two methyl rotors in the methanol dimer. As a second stage of the analysi s, a tunneling treatment taking into account all tunneling splittings is carried out. Because only K = 0 a-type transitions are considered, some ambiguity remains in the symmetry assignments and tunneling param eters reported in this work. (C) 1995 Academic Press, Inc.