PNO–CI and CEPA studies of electron correlation effects. IV. Ionization energies of the first and second row diatomic hydrides and the spectroscopic constants of their ions

Abstract

Near equilibrium potential curves for the ground states of the diatomic hydride ions LiH⁺ to HCl⁺ have been calculated from highly correlated PNO–CI and CEPA wavefunctions. The spectroscopic constants derived from the CEPA potential curves are in very good agreement with the known empirical values. Several new constants are given: r_e=1.203±0.001 Å, ω_e=2530±20 cm⁻¹, Δ G_1/2=2401±20 cm⁻¹ for BH⁺; ω_e=2851±20 cm⁻¹ for CH⁺; r_e=1.070±0.001 Å, ω_e=3059±20 cm⁻¹ for NH⁺; ω_e=1695±20 cm⁻¹, Δ G_1/2=1544±20 cm⁻¹ for AlH⁺; ω_e=2376±20 cm⁻¹ for PH⁺. The polarization minima of the potential curves of the LiH⁺ and NaH⁺ ground states are calculated deep enough to allow for several vibrational levels. The correlation contributions to the proton affinities of the first‐ and second‐row atoms have been calculated to range from −0.47 eV (for B) to +0.13 eV (for S) with expected uncertainties of about ±0.05 eV. Combination of the proton affinities with experimental atomic data and dissociation energies of the neutral hydrides yields dissociation energies of the ions with uncertainties of about ±0.05 eV and first adiabatic ionization energies with uncertainties of about ±0.1 eV. The corresponding experimental values show larger error bounds in many cases. New values are recommended for the dissociation energies (D₀) of XH⁺ and the first adiabatic ionization energies of XH, respectively, in the cases of X being Li(0.12,7.7), N(3.50,13.5), O(5.00,13.0), Na(0.12,6.9), Mg(2.00,6.9), Al(0.65,8.4), P(3.30,10.2), and S(3.70,10.2) (all values in eV).