An ab initio quartic force field of $PH3$

An ab initio quartic force field of $PH3$ is derived using the coupled-cluster theory with all singles and doubles supplemented with quasiperturbative treatment of the connected triple excitations [CCSD(T)], and Dunning’s correlation consistent polarized valence triple zeta cc-pVTZ basis set. Improved geometry and quadratic force constants are evaluated, respectively, with the correlation consistent polarized valence quadruple zeta cc-pVQZ, core–valence quadruple zeta cc-pCVQZ, and weighted core–valence quadruple zeta cc-pwCVQZ basis sets. In the latter two cases, all electrons are correlated to account for the core correlation effects. Core–valence correlation effect on geometry is found to be significant. By comparing the cc-pCVQZ and cc-pwCVQZ results with the cc-pVQZ ones, the bond length $re$ is reduced by 0.0045 or 0.0049 Å and the bond angle $θe$ by 0.07° or 0.06°, respectively. Cubic and quartic force fields are further determined with the correlation consistent polarized weighted core–valence triple zeta cc-pwCVTZ basis set. Vibrational analysis based on second-order perturbation theory is carried out with the calculated force constants. Computed fundamentals of $PH3$ agree to better than 4 cm⁻¹ on average with the experimental data. Spectroscopic constants are also predicted for a number of symmetric and asymmetric top isotopomers of $PH3.$ With a minor empirical adjustment of our best force field, agreement of 1 cm⁻¹ between the computed and experimental fundamentals is found for all isotopomers.