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-H₂³²S and Ar-H₂³⁴S, which show that the symmetrical isotopomers (with H₂S or D₂S) exist in lower and upper states giving progressions with 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-D₂³²S and D₂³⁴S have B̅'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 B̅ between lower and upper states. Perdeuteration of Ar-H₂O decreases ΔB̅ 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 ³³S quadrupolar hfs for the lower and upper states of Ar-H₂³³S, finding values for χ_aa(³³S) of −7.89 and −17.36 MHz.