			15min:

HIGH RESOLUTION INFRARED AND MICROWAVE SPECTRA OF NH₃-HCCH AND NH₃-OCS COMPLEXES: STUDIES OF WEAK C-H cdots

N HYDROGEN BOND AND ELECTRIC MULTIPOLE INTERACTIONS.

XUNCHEN LIU, YUNJIE XU, Department of Chemistry, University of Alberta, Edmonton, Canada, T6G 2G2.

C-H cdots N weak hydrogen bond is of much current interest. We report the first high resolution infrared spectroscopic study of a prototypical C-H cdots N bonded system, i.e. NH₃-HCCH, at the vicinity of the 4 band of NH₃. The spectrum has been recorded using an infrared spectrometer equipped with an astigmatic multipass cell aligned for 366 passes and a room temperature external cavity quantum cascade laser at the 6 µm region. The perpendicular band spectrum of symmetric top rotor observed is consistent with the previous microwave and infrared studies at 3 µm. We also extended the previous microwave measurement to higher J and K.

For the related NH₃-OCS complex, microwave spectrum of J up to 6 and infrared spectrum at the vicinity of the 4 band of NH₃ have been recorded and analyzed for the first time. Comparison has been made with the previously studied isoelectronic complexes such as NH₃-N₂O and NH₃-CO₂. The source of the difference will be discussed with the aid of ab~initio calculations.