Analysis and Global Fit of Tunneling Splittings in the K = 0 a-Type Microwave Spectrum of the Methanol Dimer

✍ Scribed by N. Ohashi; J.T. Hougen

• Publisher: Elsevier Science
• Year: 1995
• Tongue: English
• Weight: 669 KB
• Volume: 170
• Category: Article
• ISSN: 0022-2852
• DOI: 10.1006/jmsp.1995.1087

✦ Synopsis

Theoretical results previously developed using an internal-axis-method-like multidimensional tunneling formalism are applied to recently measured tunneling splitting patterns for (a)-type (R(J)) microwave transitions in 10 different isotopomers of the methanol dimer. Permutation-inversion group (G_{36}) species assignments for the 16 tunneling components of a given (R(J)) transition (split by 25 different tunneling motions) are presented for (0 \leqslant J \leqslant 4) for the normal isotopomer. Permutation-inversion group (G_{18}) species assignments for the 10 tunneling components of a given (R(J)) transition (split by 13 different tunneling motions) are presented for (0 \leqslant J \leqslant 3) for the two mixed ({ }^{12} \mathrm{C},{ }^{13} \mathrm{C}) isotopomers. As a first stage of the analysis, a simplified two-top treatment of suitably averaged measured line frequencies is carried out in which only the (dominant) tunneling splittings arising from internal rotation of the two methyl tops of the dimer are considered. Relatively large top-top interaction terms must be included in this two-top treatment, which is surprising in view of the large distance between the two methyl rotors in the methanol dimer. As a second stage of the analysis, a tunneling treatment taking into account all tunneling splittings is carried out. Because only (K=0)-type transitions are considered, some ambiguity remains in the symmetry assignments and tunneling parameters reported in this work. (c 1995 Academic Press, Inc.