ROTATIONAL SPECTRUM, MOLECULAR-STRUCTURE, AND HG-201 NUCLEAR-QUADRUPOLE COUPLING-CONSTANTS OF HCNHG

High resolution rotational spectra for 21 isotopic species of the hydrogen cyanide-mercury complex have been measured in the 7-15 GHz region using a Balle/Flygare pulsed Fourier transform microwave spectrometer. Rotational constants and N-14 nuclear quadrupole coupling constants are (in MHz), for (HCNHg)-N-14-Hg-202: B0=1265.6627 (7), D(J)=0.020 669(14), chi(N)=-0.695(12), and for (DCNHg)-N-14-Hg-202: B0=1201.8338(16), D(J)=0.021 213(45), and chi(N) = -0.748(19). The Hg-201 nuclear quadrupole coupling constants are, for (HCNHg)-N-15-Hg-201: -5.97(13) MHz, and for (DCNHg)-N-15-Hg-201: -6.03(24) MHz. The atomic arrangement is HCN...Hg with a zero-point vibrationally averaged center-of-mass separation of 4.05 angstrom for the most abundant (HCNHg)-N-15-Hg-202 species. The equilibrium structure was not determined. HCNHg does not exhibit the extreme centrifugal distortion and isotopic sensitivity effects seen in ArHCN [K. R. Leopold, G. T. Fraser, F. J. Lin, D. D. Nelson, Jr., and W. Klemperer, J. Chem. Phys. 81, 4922 (1984)].