Quantum Spin-Orbit Electronic State Selection of Atomic Transition Metal Vanadium Cation for Chemical Reactivity Studies.

By combining a pulsed laser ablation vanadium atom (V) beam source with the two-color laser sequential electric field pulse scheme for pulse field ionization-photoion (PFI-PI) detection, we have developed a quantum spin-orbit state selected transition metal ion source for ion-molecule reaction studies. As a demonstration, we show that the V+ ion can be prepared in the single spin-orbit levels of its three lowest quantum electronic states, V+[a5DJ ( J = 0-4), a5FJ ( J = 1-5), and a3FJ ( J = 2-4)], achieving laboratory kinetic energy ( Elab) resolutions of ≤0.2 eV. The precursor V atom beam is first excited to high- n Rydberg states by resonance-enhanced visible-ultraviolet laser photoexcitation via the V*[3d3(4F) 4s4p (3P°)] neutral intermediate state. The total photon energy is tuned in the regions from 54 380 to 63 520 cm-1 to cover the photoionization energies for the formation of these spin-orbit states. Sharp Rydberg transitions converging to the V+[a5DJ ( J = 1 and 2)] spin-orbit levels are identified in the respective PFI-PI spectra for the V+[a5DJ ( J = 0 and 1)] states. The analysis of these Rydberg members observed yields an ionization energy of 54 412.65 ± 0.15 cm-1 for V atom, which is in excellent accord with the literature value of 54 413 ± 1 cm-1 eV. In order to understand the profile for the PFI-PI spectrum of V+ ion observed and thus obtain reliable Stark shift corrections by using the sequential PFI-PI detection scheme, we have also examined the PFI-PI spectrum for Ar+(2P3/2) in detail by varying the retarding as well as the PFI electric field pulses.