THEORETICAL-STUDY OF THE PROPERTIES OF THE RADICAL PS, ITS ANION AND CATION

The properties of the diatomic thiophosphorus radical PS and its catio n and anion, in their ground electronic states, are studied using UHF, RHF, ROHF, GVB and MP2 ab initio methods with the STO-3G, 3-21G*, 6- 31G and 6-31G basis sets. As expected, the STO-3G* basis set is insuf ficient for the anion (outer molecular orbitals unbound). Most of the results obtained with the 6-31G basis set are unsatisfactory. In contr ast, the equilibrium internuclear distances (r(e)) obtained for the PS radical in all the ROHF and GVB optimizations with the 3-21G and 6-3 1G basis sets are satisfactory, the values ranging from 0.5 to 1.8% l ess than the best experimental value. The results indicate that r(e)(P S(1+)X-1 Sigma(+)) and r(e)(PS(1-) X-3 Sigma(-)) should be very close to 1.84 Angstrom and 2.03 Angstrom, respectively. The reliability of t he MP2 results varies: omega(e) for the radical and the cation are 42% higher and 6% lower than the experimental frequencies, respectively. Thus MP2 computations on these species are not warranted. The dissocia tion energy for PS X-2 Pi(r), obtained by both the GVB(3)/6-31G(5d) a nd (6d) computations is D-e = 5.0 eV, about 10% higher than the mass s pectral value, D-e = 4.6 +/- 0.1 eV. For the negative ion the computed electron affinity and dissociation energies predict that it is stable and should be observable under suitable conditions. (C) 1998 Elsevier Science B.V.