Communication: State-to-state photoionization and photoelectron study of vanadium methylidyne radical (VCH)

By employing the infrared (IR)-ultraviolet (UV) laser excitation scheme, we have obtained rotationally selected and resolved pulsed field ionization-photoelectron (PFI-PE) spectra for vanadium methylidyne cation (VCH(+)). This study supports that the ground state electronic configuration for VCH(+) is …7σ(2)8σ(2)3π(4)9σ(1) (X(2)Σ(+)), and is different from that of …7σ(2)8σ(2)3π(4)1δ(1) (X(2)Δ) for the isoelectronic TiO(+) and VN(+) ions. This observation suggests that the addition of an H atom to vanadium carbide (VC) to form VCH has the effect of stabilizing the 9σ orbital relative to the 1δ orbital. The analysis of the state-to-state IR-UV-PFI-PE spectra has provided precise values for the ionization energy of VCH, IE(VCH) = 54,641.9 ± 0.8 cm(-1) (6.7747 ± 0.0001 eV), the rotational constant B(+) = 0.462 ± 0.002 cm(-1), and the v2(+) bending (626 ± 1 cm(-1)) and v3(+) V-CH stretching (852 ± 1 cm(-1)) vibrational frequencies for VCH(+)(X(2)Σ(+)). The IE(VCH) determined here, along with the known IE(V) and IE(VC), allows a direct measure of the change in dissociation energy for the V-CH as well as the VC-H bond upon removal of the 1δ electron of VCH(X(3)Δ1). The formation of VCH(+)(X(2)Σ(+)) from VCH(X(3)Δ1) by photoionization is shown to strengthen the VC-H bond by 0.3559 eV, while the strength of the V-CH bond remains nearly unchanged. This measured change of bond dissociation energies reveals that the highest occupied 1δ orbital is nonbonding for the V-CH bond; but has anti-bonding or destabilizing character for the VC-H bond of VCH(X(3)Δ1).