State-to-state Photoionization Dynamics of Vanadium Nitride by Two-color Laser Photoionization and Photoelectron Methods

We have conducted a two-color visible-ultraviolet (VIS-UV) resonance-enhanced laser photoionization and pulsed field ionization-photoelectron (PFI-PE) study of gaseous vanadium mononitride (VN) in the total energy range of 56900–59020 cm−1. The VN molecules were selectively excited to single rotational levels of the intermediate VN(D3Π0, v′=0) state by using a VIS dye laser prior to photoionization by employing a UV laser. This two-color scheme allows the measurements of rovibronically selected and resolved PFI-PE spectra for the VN+(X2Δ; v+=0, 1, and 2) ion vibrational bands. By simulating the rotationally resolved PFI-PE spectra,J+=3/2 is determined to be the lowest rotational level of the ground electronic state, indicating that the symmetry of the ground VN+ electronic state is 2Δ3/2. The analysis of the PFI-PE spectra for VN+ also yields accurate values for the adiabatic ionization energy for the formation of VN+(X2Δ3/2), IE(VN)=56909.5±0.8 cm−1 (7.05588±0.00010 eV), the vibrational frequency ωe+=1068.0±0.8 cm−1, the anharmonicity constant ωe+χe+=5.8±0.8 cm−1, the rotational constantsBe+=0.6563±0.0005 cm−1 and αe+=0.0069±0.0004 cm−1, and the equilibrium bond length, re+=1.529 Å, for VN+(X2Δ3/2); along with the rotational constantsBe+=0.6578±0.0028 cm−1 and αe+=0.0085±0.0028 cm−1, and the equilibrium bond length re+=1.527 Å for VN+(X2Δ5/2), and the spin-orbit coupling constant A=153.3±0.8 cm−1 for VN+(X2Δ5/2,3/2). The highly precise energetic and spectroscopic data obtained in the present study are valuable for benchmarking the predictions based on state-of-the-art ab initio quantum calculations.