15min:

PANKAJ K. MANDAL AND E. ARUNAN, Department of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore- 560 012, INDIA.

Recently there has been a great deal of interest on the second row hydrides and their weakly bonded complexes and comparison to the first row hydrides. Complexes formed by H₂O and H₂S offer a wealth of information about intermolecular interaction involving first/second row hydrides. Most of the H₂O and H₂S complexes give at least two sets of rotational transitions corresponding to different internal rotor/tunneling states. In the case of Ar-H₂S complex, an anomalous substitution effect was observed. The rotational constant for Ar-D₂S was larger than that of Ar-H₂S, which is counter-intuitive. For Ar₃-H₂S, the isotope substitution effect was normal. What would be the situation for Ar₂-H₂S?

Rotational transitions (asymmetric top) were predicted on the basis of an assumed geometry (C₂v). A series of a dipole transitions have been observed for Ar₂-H₂³²S. The absence of transitions between the states whose Kp and Ko are oo and oe indicates the presence of C₂ axis interchanging two identical Ar nuclei (I=0). Twenty-one transitions have been fitted to three rotational constants and five centrifugal distortion constants and these are: A=1733.0982(11), B=1617.6570(5), C=830.2755(2) MHz; d1=9.270(5), d2=25.58(2), D_J=22.20(1), D_JK=3.34(4) and D_K=6.17(8)kHz. The rms deviation of the fit is 2.3 kHz, which is comparable to the experimental resolution. Rotational constant A is very close to that of the free Ar₂ and this is the case in most of the Ar₂-HX complexes. Assuming H₂S to be spherical, the rotational constants are fitted to give a Ar₂(c.m.) to H₂S(c.m.) distance of 3.62 Å, and this leads to an Ar! -H₂S distance of 4.09 Å, which is comparable to the Ar-H₂S distances found in Ar_m-H₂S for m = 1 and 3. One more set of transitions has been observed and it is probably due to the ground (I = 0) internal rotor state. Further studies on this state and other isotopomers are in progress. Results will be presented in the symposium.