15min:

ZHENHONG YU AND WILLIAM KLEMPERER, Department of Chemistry and Chemical Biology, Harvard University, Cambridge, MA 02138; KELLY HIGGINS, Department of Chemistry, University of Minnesota, Minneapolis, MN 55455.

The microwave spectrum of the H₂-OCS complex has been studied using molecular beam electric resonance optothermal spectrometer with 20% 40:1 H₂/OCS gas mixture in 5 atm He. This investigation is stimulated by the recent He droplet study of this species. The H₂-OCS complex has T-shaped global minimum according to a high-level ab initio potential surface calculation. We have performed bound state calculations with bound program to obtain the rotational transitions of the ground state for para -H₂-OCS complex. Several spectral transitions of ³²S and ³⁴S isomers have been measured at frequencies close to the prediction in the frequency region of 9-31 GHz. For example, two observed peaks at 10218.3 and 20385.7 MHz from H₂-OC³²S complex have been compared with the predicted 1₀₁ 0₀₀ and 2₀₂ 1₀₁ transitions at 10594.7 and 21110.2 MHz, respectively. However a number of transitions predicted were not observed although the analogous transitions in the He-OCS complex have been readily seen. In addition, small doublet splitting of near 50 KHz is observed. Since ortho -H₂ contributes to about 75 percent abundance of normal H₂ at room temperature and might bind stronger with OCS molecule than para -H₂, we believe that what we observed in this study may belongs to ortho -H₂-OCS complex. Our current experimental measurement with pure para -H₂ would provide detailed results for rotational transitions of the ground state for H₂-OCS complex in the near future.