Theoretical Study of Low-Lying Ω Electronic States of PtH and PtH+

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 Σ0++1 ground state, while the first two electronic states of PtH+ (Σ0++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.

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.

Theoretical dissociation, ionization, and spin–orbit energetics of the diatomic platinum hydrides PtH, PtH+, and PtH–

Spin–orbit configuration interaction (SO-CI) and coupled-cluster [CCSDT(Q)] theoretical methods are combined to evaluate zero-temperature thermochemical properties of PtH, PtH+, and PtH−. We obtain vibrational zero-point energies and spin–orbit stabilization energies, which lead to predictions for observable quantities: ionization energy IE(PtH) = (9.44 ± 0.07) eV; electron affinity EA(PtH) = (1.65 ± 0.04) eV; and dissociation energies D0(Pt–H) = (329.6 ± 3.9) kJ mol−1, D0(Pt+–H) = (279.3 ± 5.7) kJ mol−1, and D0(Pt−–H) = (285.0 ± 2.4) kJ mol−1 (uncertainty coverage factor = 2). Compared with available experiments, our value of D0(Pt+–H) is higher by (8 ± 8) kJ mol−1, EA(PtH) is higher by 0.15 eV, and D0(Pt–H) is lower than the upper bound by (2 ± 4) kJ mol−1.