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P. K. MANDAL, MAUSUMI GOSWAMI, E. ARUNAN, Department of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore 560 012 INDIA.
Rotational spectra of Ar(H2S)2 and Ar(D2S)2 complexes have been observed with a pulsed nozzle Fourier transform microwave spectrometer. About 40 a and b dipole transitions have been observed for each isotopomer. Each transition is spilt in to two as observed earlier by Lovas for the (H2S)2 complex . 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 = 1566.27(3) MHz and C = 826.817(4) MHz. The C rotational constants for the two states were nearly identical, for both isotopomers. The A and B rotational constants for the upper state of Ar(H2S)2 are about 10 MHz and 6 MHz larger than those for the lower state. However, for Ar(D2S)2, A and B rotational constants for the upper state were larger only by 30 kHz and 50 kHz, respectively. This is in contrast to the very similar splittings observed in B rotational constants for (H2S)2 (1.2 MHz) and (D2S)2 (0.9 MHz). Assuming H2S to be a sphere, the c.m. separation between two H2S units is calculated to be 4.03 Å which is 0.1 Å less than that found in (H2S)2 dimer. The distance between Ar and c.m. of (H2S)2 is 3.55 Å and the Ar-c.m.(H2S) distance is 4.09 Å. Ab initio calculations at MP2 level using various basis sets lead to three distinct minima including a pseudo-linear local minimum. At MP2/6-311++G(3df,2p) level of theory, the global minimum has a structure having Ar along the 'c' axis of (H2S)2.