Ab initio spectroscopy and thermochemistry of the platinum hydride ions, PtH+ and PtH−.

Rovibrational levels of low-lying electronic states of the gas-phase, diatomic molecules, PtH⁺ and PtH⁻, are computed on potential-energy functions obtained by using a hybrid spin–orbit configuration-interaction procedure. PtH⁻ has a well-separated Σ 0 + + 1 ground state, while the first two electronic states of PtH⁺ ( Σ 0 + + 1 and ³Δ₃) are nearly degenerate. Combining the experimental photoelectron (PE) spectra of PtH⁻ with theoretical photodetachment spectroscopy leads to an improved value for the electron affinity of PtH, EA(PtH) = (1.617 ± 0.015) eV. When PtH⁻ is a product of photodissociation of PtHCO₂⁻, its PE spectrum is broad because of rotational excitation. Temperature-dependent thermodynamic functions and thermochemistry of dissociation are computed from the theoretical energy levels. Previously published energetic quantities for PtH⁺ and PtH⁻ are revised. The ground ¹Σ⁺ term of PtH⁺ is not well described using single-reference theory. [ABSTRACT FROM AUTHOR]