MICROWAVE SPECTRUM OF THE H2S DIMER: OBSERVATION OF Ka=1 LINES

Large amplitude tunneling motions in (chem{H_2S})$_{2}$ complicate the analysis of its microwave spectrum. The previous rotational spectrum of (chem{H_2S})$_{2}$ was observed using the Balle-Flygare pulsed nozzle FT microwave spectrometers at NIST and IISc. For most isotopomers of (chem{H_2S})$_{2}$ a two state pattern of a-type K$_{a}$=0 transitions had been observed and were interpreted to arise from E$_{1}$$^{+/-}$ and E$_{2}$$^{+/-}$ states of the six tunneling states expected for (chem{H_2S})$_{2}$. K$_{a}$=0 lines gave us only the distance between the acceptor and donor S atoms.footnote {F. J. Lovas, P. K. Mandal and E. Arunan, unpublished work}_x000d_ footnote {P. K. Mandal Ph.D. Dissertation, Indian Institute of Science, (2005)}_x000d_ footnote {F. J. Lovas, R. D. Suenram, and L. H. Coudert. 43rd Int.Symp. on Molecular Spectroscopy. (1988)}. The (B+C)/2 for E$_{1}$ and E$_{2}$ states were found to be 1749.3091(8) MHz and 1748.1090(8) MHz respectively. In this work, we have observed the K$_{a}$=1 microwave transitions which enable us to determine finer structural details of the dimer. The observation of the K$_{a}$=1 lines indicate that (chem{H_2S})$_{2}$ is not spherical in nature, their interactions do have some anisotropy. Preliminary assignment of K$_{a}$=1 lines for the E$_{1}$ state results in B=1752.859 MHz and C=1745.780 MHz. We also report a new progression of lines which probably belongs to the parent isotopomers._x000d_ _x000d_ _x000d