Rotational spectra, structure, and internal dynamics of Ar–H2S isotopomers

Abstract

Several groups have studied the rotational spectra of various isotopomers of the pseudolinear Ar–H2S dimer. We have found two additional K=0 progressions, for Ar–H2 32S and Ar–H2 34S, which show that the symmetrical isotopomers (with H2S or D2S) exist in lower and upper states giving progressions with B̄ differing by about 50 MHz. When assigned and analyzed on this basis, the overall spectra are quite similar to those of the Ar–H2O analogue where the doubling is caused by 000 and 101 internal rotor states of the H2O or D2O. Such states of the H2S most likely cause the doubling found in the Ar–H2S isotopomers. However, some of the details differ in interesting ways, indicating substantial differences in their potential energy surfaces. The lower states of Ar–D2 32S and D2 34S have B̄’s about 28 MHz larger than those for H2S, while the isotopomers of the upper states exhibit a more normal decrease of about 12 MHz. Somewhat related to this is the effect of deuteration on the difference in B̄ between lower and upper states. Perdeuteration of Ar–H2O decreases ΔB̄ from 76 to 68 MHz. The corresponding change for Ar–H2S is much larger, from 44 to 5 MHz. For the internal rotor model, analysis of the hfs for Ar–H2O/D2O assigns its upper and lower states to 000 and 101 rotor states of the water, respectively. But this assignment is reversed in Ar–H2S/D2S. Also, we have observed and fitted the S33 quadrupolar hfs for the lower and upper states of Ar–H2 33S, finding values for χaa(33S) of −7.89 and −17.36 MHz.