Pulsed field ionization zero kinetic energy photoelectron spectroscopy of the vanadium dimer molecule

The technique of pulsed-field-ionization zero-kinetic-energy (PFI-ZEKE), photoelectron spectroscopy was employed to probe the electronic structure of the V₂⁺ cation. Rotationally resolved PFI-ZEKE spectra of the V₂⁺ ground state were obtained by two color excitation via the 700 nm A ³Π_u←X ³Σ _g^- system. The observation of transitions from the A ³Π2_u state to two spin-orbit components with Ω=1/2 and Ω=3/2, confirms that the cation ground state has 4Σ_g^- symmetry, in accordance with previous experimental and theoretical work. Striking differences were observed in the rotational selection rules for the ⁴Σ_g ^-←A ³Π^1u and the ⁴Σ _g¹←A ³Π_2u transitions. The adiabatic ionization potential of V₂ was determined to be 51 271.14(50) cm^-1. From an analysis of the rotational structure of the PFI-ZEKE spectra, the following molecular constants were determined for the ⁴Σ_g¹ state: r₀=1.7347(24) Å, second order spin-orbit splitting, λ=5.248(17) cm^-1, spin-rotation constant, γ=0.0097(87) cm^-1, T₀=51 282.20(50) cm^-1 (1σ error bounds).