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.