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Rotational Spectra of phenylacetylene-$H2S$, phenylacetylene-$HDS$, phenylacetylene-$D2S$, phenylacetylene-$H234S$, $C8H5D-H2S$ have been measured. The spectra were recorded using a Balle-Flygare type PNFT Microwave spectrometer[1]. Helium was used as a carrier gas for these measurements. Both $a$' and $b$' dipole transitions have been observed. For the parent isotopomer, all the transitions are split into two. The rotational spectra of phenylacetylene-$HDS$ indicate that the splitting is due to the interchange of equivalent hydrogens of $H2S$ unit in the complex. The measured rotational constants of the parent species are $A=1206.551(7)MHz$, $B=1134.152(6)MHz$, $C=732.192(6)MHz$ for the stronger series and $A=1206.732(7)MHz$, $B=1134.056(6)MHz$, $C=732.141(8)MHz$ for the weaker series. The constants derived from the experiments confirm a structure where $H2S$ is placed perpendicular to the plane of the phenylacetylene molecule. This study reveals that the binding of $H2O$ and $H2S$ to the phenylacetylene molecule is very different. Microwave spectroscopic investigations confirmed that $H2O$ prefers to be in plane of the phenylacetylene, donating one of its hydrogen to the acetylenic $\pi$ cloud while the oxygen of $H2O$ is involved in a secondary interaction forming C-H---O hydrogen bond with the ring hydrogen ortho to the acetylenic group[2]. \bigskip 1. Arunan et al.{\it Current Science},82(2002)533. \smallskip 2. TA04,{\it 63rd International Symposium on Molecular Spectroscopy},Columbus, June 16-20, 2008.