AB-INITIO CALCULATIONS ON MONOHALOGENOPHOSPHANES PH(2)X (X=F,CL,BR,I), AND EXPERIMENTAL DETECTION AND CHARACTERIZATION OF PH2F AND PH2CL BYHIGH-RESOLUTION INFRARED-SPECTROSCOPY

The harmonic and anharmonic force fields of the title compounds have b een calculated at the ab initio self-consistent-field level using effe ctive core potentials and polarized double-zeta basis sets. Additional calculations for PH2F employ larger basis sets and include electron c orrelation. Many rovibrational constants are predicted theoretically. The infrared spectra generated from the ab initio data have guided the experimental identification of PH2F and PH2Cl in the gas phase. High resolution Fourier transform infrared spectra of these unstable molecu les have been recorded for the first time. Rotational analyses for sev eral bands are reported which provide-accurate ground state constants and a precise characterization of a number of vibrationally excited st ates. The accuracy of the ab initio predictions for PH2F and PH2Cl is evaluated by comparisons with these experimental data.