J dependence of χa(14N) and χa(83Kr) for the Kr–HCN dimer

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Abstract
High‐resolution microwave rotational spectra for 84Kr–HCN, 86Kr–HCN, and 83Kr–HC15N 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. 7 8, 3483 (1983)] over a wider frequency range (2–18 GHz) and with higher resolution. The 14N nuclear quadrupole coupling constant has been found to increase linearly with J(J+1) for 84Kr–HCN and 86Kr–HCN, with the slope Dχ one‐third its value for the analogous Ar–HCN dimer. For 84Kr–HCN, the average HCN bending amplitude θ decreases from 26.85° for J=0 to 26.28° for J=7, while the average Kr to HCN center‐of‐mass (c.m.) distance R increases from 4.5202 to 4.5246 Å. Similar results are found for 86Kr–HCN. In addition, the 83Kr quadrupole coupling constant for 83Kr–HC15N 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 χa(83Kr) is consistent with the J dependencies of θ and R inferred from χa(14N) in the 14N species. Radial and angular motions of HCN are strongly coupled.