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Rotational Spectra and Structure of the $Ar_2-H_2S$ Complex: Pulsed Nozzle Fourier Transform Microwave Spectroscopic and Ab Initio Studies

Mandal, Pankaj K and Ramdass, Dharmender J and Arunan, E (2004) Rotational Spectra and Structure of the $Ar_2-H_2S$ Complex: Pulsed Nozzle Fourier Transform Microwave Spectroscopic and Ab Initio Studies. In: Physical Chemistry Chemical Physics, 7 (14). pp. 2740-2746.


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This paper reports the rotational spectrum and structure of the $Ar_2-H_2S$ complex and its HDS and D2S isotopomers. The ground state structure has heavy-atom $C_2_v$ symmetry with the two Ar atoms indistinguishable and $H_2S$ freely rotating as evinced by the fact that asymmetric top energy levels with $K_p$ odd levels are missing. The rotational constants for the parent isotopomer are: A = 1733.115(1) MHz, B = 1617.6160(5) MHz and C = 830.2951(2) MHz. Unlike the $Ar_2-H_2S$ complex, the $Ar_2-H_2S$ does not show an anomalous isotopic shift in rotational constants on deuterium substitution. However, the intermolecular potential is still quite .oppy, leading to very di.erent centrifugal distortion constants for the three isotopomers. The Ar-Ar and Ar-c.m.$(H_2S)$ distances are determined to be 3.820 A and 4.105 A, respectively. The A rotational constants for $Ar_2-H_2S/HDS/ D_2S$ isotopomers are very close to each other and to the B constant of free $Ar_2$, indicating that $H_2S$ does not contribute to the moment of inertia about the a-axis. Ab initio calculations at MP2 level with aug-cc-pVQZ basis set lead to an equilibrium $C_2v$ minimum structure with the Ar-Ar line perpendicular to the H-H line and the S away from $Ar_2$. The centrifugal distortion constants, calculated using the ab initio force .eld, are in reasonable agreement with the experimental values. However, they do not show the variation observed for di.erent isotopmers. The binding energy of $Ar_2-H_2S$ has been determined to be 507 cm$^-^1$ $(6.0 kJ mol^-^1)$ by CBS extrapolation after correcting for basis set superposition error. Potential energy scans point out that the barrier for internal rotation of $H_2S$ about its b axis is only $10 cm^1$ and it is below the zero point energy $(13.5 cm^-^1)$ in this torsional degree of freedom. Internal rotation of $H_2S$ about its a- and c-axes also have small barriers of about $50 cm^-^1$ only, suggesting that $H_2S$ is extremely .oppy within the complex.

Item Type: Journal Article
Publication: Physical Chemistry Chemical Physics
Publisher: Royal Society of Chemistry
Additional Information: The copyright for this article belongs to Royal Society of Chemistry.
Department/Centre: Division of Chemical Sciences > Inorganic & Physical Chemistry
Date Deposited: 05 Aug 2005
Last Modified: 19 Sep 2010 04:19
URI: http://eprints.iisc.ac.in/id/eprint/3404

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