IDENTIFICATION AND CHARACTERIZATION OF THE GAS-PHASE COMPLEX HCN...CL2 BY ROTATIONAL SPECTROSCOPY

The ground-state rotational spectra of three isotopomers, HC N-15...Cl-35(2), HC N-15...Cl-35 Cl-35 and HC N-15...Cl-25 Cl-37, of the linear complex HCN...Cl2 have been observed by the pulsed-nozzle, Fourier-transform microwave technique and analysed to give the rotational constant B(o), the centrifugal distortion constant D(J), and the chlorine nuclear quadrupole coupling constants chi(Cl(i)) and chi(Cl(o)) in each case. A B(o) value has also been estimated for the isotopomer HC N-14...Cl-35(2). The distances r(N...Cl(i)), r(N...Cl(o)) and r(Cl-Cl) have been determined from the rotational constants (i denotes 'inner', o, 'outer'). The small value of k(sigma), the intermolecular stretching force constant, estimated from D(J), and the small difference DELTA(chi)(Cl-35) = chi(Cl-35(i)) - chi(Cl-35(o)) are interpreted in terms of only a small perturbation of the Cl2 subunit on complex formation. A comparison of the properties of the four dimers B...Cl2, where B = CO, HF, PH3 and HCN, with those of the corresponding series B...HCl of hydrogen-bonded complexes indicates a parallel behaviour in the two series. The propensity of Cl2 to form complexes with B, as measured by its gas-phase electrophilicity E, is compared with that of HCl.