Structure and thermodynamic stability of the OsC and OsC2 molecules by theoretical calculations and by Knudsen cell mass spectrometry

Knudsen cell mass spectrometric equilibrium measurements together with theo retical computations have been employed to gain structural and thermodynami c information of the OsC and OsC2 molecules. Several levels of theory have been applied to determine the structures, molecular parameters, and physico -chemical properties of OsC(g) and OsC2(g), and their singly charged ions. Complete active space self-consistent field (CASSCF) calculations were perf ormed on the apparent (3)Sigma (-) ground state and first (3)Delta excited state of OsC. From the analyzed gaseous equilibria and the thermal function s calculated from the computed molecular parameters, the following atomizat ion enthalpies, Delta H-a(0)o(OsC,g) and Delta H-a(0)o(OsC2,g), and enthalp ies of formation, Delta H-f(298.15)o(OsC,g) and Delta H-f(298.15)o(OsC2,g), in kJ mol(-1), have been obtained: OsC, 605.6+/-14.0 and 895.4+/-14.0; OsC 2, 1154.6+/-18.0 and 1059.5+/-18.0. The results have been compared with tho se for the other platinum metal carbides and oxides. (C) 2001 American Inst itute of Physics.