AB-INITIO GEOMETRY, QUARTIC FORCE-FIELD, AND VIBRATIONAL FREQUENCIES FOR P-4

We have computed the equilibrium bond length and quartic force field f or tetrahedral P-4 using coupled-cluster methods and a variety of exte nded basis sets. Our calculations include the effect of correlating co re, as well as valence, electrons. As with earlier P-4 studies, our co mputed 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-pha se spectroscopic studies of P-4. Our calculated endothermicity relativ e to two P-2 molecules appears to be well converged with respect to co rrelation treatment and basis set, but again differs substantially fro m present experimental values, which we speculate are underestimates. (C) 1997 American Institute of Physics.