Ab initio spectroscopy and thermochemistry of diatomic platinum hydride, PtH.

Rovibrational levels of low-lying electronic states of the diatomic molecule PtH are computed using non-relativistic wavefunction methods and a relativistic core pseudopotential. Dynamical electron correlation is treated at the coupled-cluster with single and double excitations and a perturbative estimate of triple excitations level, with basis-set extrapolation. Spin-orbit coupling is treated by configuration interaction in a basis of multireference configuration interaction states. The results compare favorably with available experimental data, especially for low-lying electronic states. For the yet-unobserved first excited state, Ω = 1/2, we predict constants including Te = (2036 ± 300) cm-1 and ΔG1/2 = (2252.5 ± 8) cm-1. Temperature-dependent thermodynamic functions, and thermochemistry of dissociation, are computed from the spectroscopic data. The ideal-gas enthalpy of formation is ΔfH298.15o(PtH) = (449.1 ± 4.5) kJ mol-1 (uncertainties expanded by k = 2). The experimental data are reinterpreted, using a somewhat speculative procedure, to yield the bond length Re = (1.5199 ± 0.0006) Å.