J-DEPENDENCE OF CHI-A(N-14) AND CHI-A(KR-83) FOR THE KR-HCN DIMER

High-resolution microwave rotational spectra for (Kr-HCN)-Kr-84, (Kr-HCN)-Kr-86, and (Kr-HCN)-Kr-83-N-15 have been observed with the pulsed-nozzle, Fourier transform Balle/Flygare Mark II spectrometer. A new method of injecting the gas sample into the Fabry-Perot cavity along the axis of the microwave pulse was used for some transitions to narrow the linewidths. The present work extends that of the original study [J. Chem. Phys. 78, 3483 (1983)] over a wider frequency range (2-18 GHz) and with higher resolution. The N-14 nuclear quadrupole coupling constant has been found to increase linearly with J(J + 1) for (Kr-HCN)-Kr-84 and (Kr-HCN)-Kr-86, with the slope D-chi one-third its value for the analogous Ar-HCN dimer. For (Kr-HCN)-Kr-84, the average HCN bending amplitude theta-decreases from 26.85-degrees for J = 0 to 26.28-degrees for J = 7, while the average Kr to HCN center-of-mass (c.m.) distance R increases from 4.5202 to 4.5246 angstrom. Similar results are found for (Kr-HCN)-Kr-86. In addition, the Kr-83 quadrupole coupling constant for (Kr-HCN)-Kr-83-N-15 is dependent on J, increasing from 7.5382 MHz for J = 1 to 7.5713 MHz for J = 4. This is interpreted with the long-range polarization model used previously to explain rare gas nuclear quadrupole coupling constants in Rg-HX dimers. In particular, the J dependence observed for chi-a (Kr-83) is consistent with the J dependencies of theta and R inferred from chi-a (N-14) in the N-14 species. Radial and angular motions of HCN are strongly coupled.