V-3: Structure and vibrations from density functional theory, Franck-Condon factors, and the pulsed-field ionization zero-electron-kinetic energy spectrum

Density functional calculations of neutral and cationic vanadium trimers ar e presented. The all-electron calculations employed a gradient-corrected ex change-correlation functional and a newly developed vanadium basis set opti mized for gradient-corrected density functional calculations. For both neut ral and charged systems, different isomers were studied in order to determi ne the lowest energy structures. A vibrational analysis was performed in or der to characterize these isomers. We found an equilateral triangle (2)A(1) ' ground state for V-3 and an equilateral triangle (3)A(2)' ground state fo r V-3(+). The experimental pulsed-field ionization zero-electron-kinetic en ergy spectrum was simulated by calculating multidimensional Franck-Condon f actors, using the geometries and harmonic frequencies of the calculated min ima of V-3 and V-3(+). The excellent agreement between the experimental and theoretical spectra allows the unequivocal determination of the ground sta te structure of V-3. This work provides a final answer to the controversy i n the literature about the ground state structure of V-3 and yields deeper insight into the electronic structure of the neutral and cationic systems. (C) 2001 American Institute of Physics.