The (X)over-tilde B-2(1), B-2(2), (2)A(1), and (2)A(2) states of oxygen difluoride cation (F2O+): High-level ab initio calculations and simulation ofthe ultraviolet photoelectron spectrum of F2O

The ultraviolet photoelectron spectrum of F2O was recorded with a higher re solution than previously published. New vibrational structure was observed in the second and third bands. Near state-of-the-art molecular orbital calc ulations were performed on the (X) over tilde (1)A(1) state of F2O and the (X) over tilde B-2(1), B-2(2), (2)A(1), and (2)A(2) state of F2O+, and thei r potential energy functions were computed. Spectral simulations based on F ranck-Condon factor calculations including the Duchinsky effect were carrie d out within the harmonic oscillator model and also with the inclusion of a nharmonicity, in order to assist spectral assignment. Based on the computed ionization energies obtained with the coupled cluster and multireference c onfiguration interaction methods with basis sets of up to quintuple zeta qu ality, the order of the low-lying cationic states of F2O+ has been firmly e stablished. However, the detailed assignment of the overlapping second and third photoelectron bands was only achieved with the aid of spectral simula tion. The iterative Franck-Condon analysis (IFCA) procedure was carried out for the first band {F2O+ ((X) over tilde B-2(1))<--F2O ((X) over tilde (1) A(1))} in the photoelectron spectrum. With the geometrical parameters of F2 O ((X) over tilde (1)A(1)) being fixed at the available experimental values , geometrical parameters of the (X) over tilde B-2(1) state of F2O+ were de rived. Based on anharmonic Franck-Condon factor calculations, the recommend ed IFCA geometrical parameters for the ground state of F2O+ are R(FO) = 1.3 23 +/-0.002 Angstrom and angle FOF=107.3 +/-0.2 degrees. (C) 2001 American Institute of Physics.