15min:
REASSIGNMENT OF MILLIMETERWAVE SPECTRUM OF THE HCN INTERNAL ROTATION BANDS OF H2-HCN.

KENSUKE HARADA, RISA YAMANAKA AND KEIICHI TANAKA, Department of Chemistry, Faculty of Sciences, Kyushu University, Fukuoka, 812-8581 JAPAN.

The H2-HCN complex is a weakly bound molecular complex and we have reported the pure rotational transitions of H2-HCN in the MMW region. According to the results, ortho- and para-H2 complexes have different structures in the ground state, H2 is attached to the nitrogen and hydrogen end of HCN, respectively, for ortho- and para-H2 complexes and the Sigma symmetry has been confirmed for both species.

We also reported the MMW spectroscopy of j=1-0 internal rotation band of H2-HCN in 2006 , where j is the quantum number for the HCN internal rotation. Although we assigned most of intense lines to the Sigma1- Sigma0 and Pi1- Sigma0 bands of (ortho)H2-HCN, some intense lines are unidentified. To confirm their assignments, we performed the MMW-MMW double resonance spectroscopy in the present study and came to the conclusion that our previous assignments of Sigma1- Sigma0 and Pi1- Sigma0 bands should be changed, and then all of the intense lines are finally assigned to the Pi1- Sigma0 (R0, R1,R2, Q1, Q2, and P2) and Sigma1- Sigma0 (R0, and P2) bands.

The band origins of the Sigma1- Sigma0 and Pi1- Sigma0 bands of (ortho)H2-HCN newly determined are 187 and 165 GHz, respectively. They are larger than those of Ne-HCN (133 and 107 GHz) but comparable with those of Ar-HCN (165 and 182 GHz, their order is reversed) indicating that the potential anisotropy of (ortho)H2-HCN is larger than that of Ne-HCN but comparable with that of Ar-HCN. The mean square amplitudes of HCN for excited states ( 57o and 51o for Sigma1 and Pi1), given by the analysis of hyperfine structure of the nitrogen nucleus, are much larger than that (33o) of the ground Sigma0 state.

A plenty of weak lines in the 100-300 GHz region are still unassigned, possibly due to the higher internal rotation bands of ortho-H2 complex, such as the Delta1- Pi0 band, as well as the fundamental bands ( Sigma1- Sigma0 and Pi1- Sigma0) of para-H2 complex. Analysis of these weak bands and survey in the region with pure para-H2 sample are now in progress.