Rotationally resolved state-to-state photoionization and the photoelectron study of vanadium monocarbide and its cations (VC/VC+)

Abstract

By employing two-color visible (VIS)-ultraviolet (UV) laser photoionization and pulsed field ionization-photoelectron (PFI-PE) techniques, we have obtained highly rotationally resolved photoelectron spectra for vanadium monocarbide cations (VC⁺). The state-to-state VIS-UV-PFI-PE spectra thus obtained allow unambiguous assignments for the photoionization rotational transitions, resulting in a highly precise value for the adiabatic ionization energy (IE) of vanadium monocarbide (VC), IE(VC) = 57512.0 ± 0.8 cm⁻¹ (7.13058 ± 0.00010 eV), which is defined as the energy of the VC⁺(X³Δ₁; v⁺ = 0; J⁺ = 1) ← VC(X²Δ_3/2; v′′ = 0; J′′ = 3/2) photoionization transition. The spectroscopic constants for VC⁺(X³Δ₁) determined in the present study include the harmonic vibrational frequency ω_e⁺ = 896.4 ± 0.8 cm⁻¹, the anharmonicity constant ω_e⁺x_e⁺ = 5.7 ± 0.8 cm⁻¹, the rotational constants B_e⁺ = 0.6338 ± 0.0025 cm⁻¹ and α_e⁺ = 0.0033 ± 0.0007 cm⁻¹, the equilibrium bond length r_e⁺ = 1.6549 ± 0.0003 Å, and the spin–orbit coupling constant A = 75.2 ± 0.8 cm⁻¹ for VC⁺(X³Δ_1,2,3). These highly precise energetic and spectroscopic data are used to benchmark state-of-the-art CCSDTQ/CBS calculations. In general, good agreement is found between the theoretical predictions and experimental results. The theoretical calculations yield the values, IE(VC) = 7.126 eV; the 0 K bond dissociation energies: D₀(V–C) = 4.023 eV and D₀(V⁺–C) = 3.663 eV; and heats of formation: , , , and kJ mol⁻¹.