V3:: 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 are presented. The all-electron calculations employed a gradient-corrected exchange-correlation functional and a newly developed vanadium basis set optimized for gradient-corrected density functional calculations. For both neutral and charged systems, different isomers were studied in order to determine the lowest energy structures. A vibrational analysis was performed in order 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 for V-3(+). The experimental pulsed-field ionization zero-electron-kinetic energy spectrum was simulated by calculating multidimensional Franck-Condon factors, using the geometries and harmonic frequencies of the calculated minima of V-3 and V-3(+). The excellent agreement between the experimental and theoretical spectra allows the unequivocal determination of the ground state structure of V-3. This work provides a final answer to the controversy in 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.