Ab initio geometry, quartic force field, and vibrational frequencies for P-4

We have computed the equilibrium bond length and quartic force field for tetrahedral P-4 using coupled-cluster methods and a variety of extended basis sets. Our calculations include the effect of correlating core, as well as valence, electrons. As with earlier P-4 studies, our computed results show significant differences with current experimental estimates of both bond length and fundamental vibrational frequencies: possible reasons for this disagreement are discussed, with particular reference to the effects of the elevated temperatures used in gas-phase spectroscopic studies of P-4. Our calculated endothermicity relative to two P-2 molecules appears to be well converged with respect to correlation treatment and basis set, but again differs substantially from present experimental values, which we speculate are underestimates. (C) 1997 American Institute of Physics.