The torsional and asymmetry splittings in HSOH

Abstract We refine the analytic treatment developed by Yamada et al. [K.M.T. Yamada, G. Winnewisser, P. Jensen, J. Mol. Struct. 695–696 (2004) 323] to explain the torsional splittings observed for HSOH. Here we find that in addition to the cis - and trans -tunnelling matrix elements, W c and W t , the parameter originating from the torsion-rotation cross-term, ξ J ^ τ J ^ z , is also important. The torsional splittings of HSOH have a peculiar nature in that their magnitudes change cyclically with K with a period of approximately three. The previous treatment reproduced one cycle of this variation. Adjusting the three parameters of the current version to experimental data, which now extend to K = 5 , the calculated splittings reproduce the experimental results quite well. The cyclic pattern is now calculated to extend over at least three cycles.