Pulsed nozzle Fourier transform microwave spectroscopic and ab initio investigationson the weakly bound Ar-(H2S)2 trimer

Abstract

A pulsed nozzle Fourier transform microwave spectrometer has been used to obtain the rotational spectra of Ar-(H2S)2 and Ar-(D2S)2 trimers. Two states have been observed for each trimer and these are likely to arise due to tunneling/internal rotation of the two H2S monomers within the trimer. The rotational constants for the lower state of Ar-(H2S)2 are: A = 1810.410(6) MHz; B = 1596.199(9) MHz and C = 848.814(2) MHz; and those for Ar-(D2S)2 are A = 1725.49(1) MHz; B = 1566.26(2) MHz; and C = 826.818(3) MHz. From these rotational constants, the Ar-H2S and H2S-H2S distances have been estimated to be 4.04 and 4.08 A, respectively. The splitting observed between the two states is of the order of a few MHz for Ar-(H2S)2 and a few kHz for Ar-(D2S)2. Ab initio calculations at MP2 level with large basis sets up to aug-cc-PVQZ level lead to three different minima, including a pseudo-linear one. Experimental rotational constants are consistent with the other two T-shaped structures in which Ar approaches the (H2S)2 along either its B or C axis. Single-point calculations at CCSD(T)/aug-cc-pVTZ level identifies the global minimum as having Ar along the B/C axis of (H2S)2 and it has a stabilization energy of 1.0 kcal mol-1, after zero-point and counter-poise corrections.