Internal rotation tunnelling in HSOH

Experimental spectra of HSOH exhibit splittings caused by torsional tunnelling between two equivalent, enantiomer minima. We aim at explaining the observed variation of these splittings with the rotational quantum number Ka [Chem. Eur. J. (2004); J. Mol. Spectrosc. 221 (2003) 121] in terms of a relatively simple, parameterized model developed by following ideas of Hougen [Can. J. Phys. 62 (1984) 1392; J. Mol. Spectrosc. 98 (1983) 375]. We have derived expressions for the torsional splittings of HSOH. Unfortunately, these expressions contain so many adjustable parameters that the available experimental data are not sufficient to determine the corresponding values. By making additional approximations we can, however, obtain a model that reproduces the observed splittings. q 2004 Elsevier B.V. All rights reserved.