A STRUCTURAL STUDY OF THE $H_{2}S\cdot CO_{2}$ VAN DER WAALS COMPLEX

Author Institution: Naval Research Laboratory, Washington, DC 20375-5000.; Molecular Spectroscopy, NIST, Gaithersburg, MD 20899.; Institute for Physical Chemistry, U. of Kiel; University of Arizona, Tucson, AZ 85721The rotational spectra of $H_{2}S$$CO_{2}$ and two deuterated forms have been observed using a pulsed beam Fourier transform microwave spectrometer. For each of the three complexes we assign a-type and c-type transitions which are split into a ``weak'' and a ``strong'' intensity component. The analysis based on that previously used for the $(H_{2}O)_{2}$ complex and modified for application to $H_{2}S\cdot CO_{2}$ allowed us to assign two internal rotations within the complex. The following rotational constants were determined: $$\begin{array}{llll}&A (MHz)& B (MHz)& C (MHz)\\ H_{2}S\cdot CO_{2} &10783.54 (18)& 2147.63 (17) &1806.61 (17)\\ HDS\cdot CO_{2} & 10782.94 (4200)& 2107.26 (23)& 1775.88 (23)\\ D_{2}S\cdot CO_{2} & 10359.39 (600) &2065.37 (1) &1746.09 (1)\\\end{array}$$ Two structures are possible for the complex. Both have the $CO_{2}$ and the S atom of $H_{2}S$ in a T-shaped configuration. The $H_{2}S$ plane is situated out of the $CO_{2}$-S plane with the hydrogens pointing either toward ($\Theta = 64^{\circ}$) or away ($\Theta = 116^{\circ}$) from the $CO_{2}$. This is determined by assuming the total dipole moment. $\mu_{T}$, for $H_{2}S\cdot CO_{2}$ the complex ($T=0.918 (24) D$) is due to the $H_{2}S$ dipole ($\mu_{b}=H_{2}S)=0.9783$). For either the $\Theta=64^{\circ}$ or $\Theta=116^{\circ}$ structure the $R_{cm}$ bond distance for $H_{2}S\cdot CO_{2}$ is 3.494(24){\AA}. The importance of the structure of this complex to applications in the area of bimolecular reaction dynamics will be discussed