MICROWAVE-SPECTRA AND STRUCTURE OF HCN-BF3 - AN ALMOST WEAKLY-BOUND COMPLEX

Rotational spectra of the complex HCN-BF3 have been observed using pul sed-nozzle Fourier transform microwave spectroscopy. Spectra have been observed for the B-11 and B-10 species with both (HCN)-N-14 and (HCN) -N-15, and the hyperfine structure has been analyzed. The complex has the expected C3v structure, with the nitrogen end of the HCN toward th e boron, but the observed BN bond length of 2.473(29) angstrom is nota bly shorter than that in the related weakly bound systems N=N-BF3 and N=C-C=N-BF3. The out-of-plane distortion of the BF3 cannot be determin ed accurately but is probably less than 3-degrees. We compare the stru cture, force constants, quadrupole coupling constants, and binding ene rgy of the complex with those of other species formed from BF3 and a v ariety of nitrogen donors. Despite the rather short B-N bond length, t he force constant for the intermolecular bond, as well as the boron an d nitrogen nuclear quadrupole coupling constants, is comparable to tho se of a truly weakly bound system.