15min:
ROTATIONAL SPECTRA OF THE H2-HCN COMPLEX OBSERVED BY FOURIER-TRANSFORM MICROWAVE SPECTROSCOPY. THE INTERNAL ROTATION OF H2 IN THE H2-HCN COMPLEX..

M. ISHIGURO, K. HARADA, KEIICHI TANAKA AND T. TANAKA, Department of Chemistry, Faculty of Science, Kyushu University, Fukuoka, 812-8581 Japan; Y. SUMIYOSHI AND Y. ENDO, Department of Pure and Applied Sciences, Graduate School of Arts and Sciences, The University of Tokyo, Komaba, Meguroku, Tokyo, 153-8902, Japan.

Fourier-Transform Microwave (FTMW) spectroscopy has been applied to the observation of the J=1-0 rotational lines of the H2-HCN and H2-DCN complexes for the ortho- and para-H2 species. The rotational constants derived for the HCN/DCN complexes support definitely that H2 is attached to the N end of HCN for the ortho-H2 species, while H2 is attached to the H end of HCN for the para-H2 species, consistent with the recent vibrational spectra in the He-droplet . The nuclear quadrupole interaction constants of the nitrogen nucleus (I_\textup\tinyN = 1) show that the HCN/DCN part executes a floppy motion with a large mean amplitude.

The splitting due to the magnetic hyperfine interaction of the H2 part was observed for ortho-H2-HCN (j=1 for H2 internal rotation) thanks to the high resolution of FTMW spectroscopy, but not for para-H2-HCN (j=0 for H2 internal rotation). Because of Sigma symmetry of the ortho-H2-HCN complex in the ground state, nuclear spin-nuclear spin interaction contributes to the hydrogen hyperfine interaction, but not the nuclear spin-rotation intraction. The magnetic interaction constant dH for ortho-H2-HCN was determined to be 54.6(38) kHz. The value corresponds to 94.7% of that of free hydrogen molecule 57.671(24) kHz , indicating almost free rotation of the H2 part in the complex. The spectrum of ortho-H2-DCN shows also the splitting due to the magnatic hyperfine interaction of H2, but the hyperfine partern is more complicated because of the nuclear quadrupole interaction of the D atom (I_\textup\tinyD = 1). The magnetic interaction constant for ortho-H2-DCN indicates that H2 is rotating almost freely in the complex as well.