Journal of Chemical Physics, Vol.108, No.18, 7684-7694, 1998
Ab initio studies on the electronic excited states and photodissociation of O-3 anion
Extensive ab initio calculations have been performed for the low-lying electronic states of O-3(-) to elucidate the mechanism of photodissociation processes. The identity of the mysterious state implied by the recent experiment of Continetti ct nl. has been discussed based on the current calculations. Calculations reveal that B-2(2) is a truly bound state favoring a strongly bent geometry with angle O-O-O similar to 90.0 degrees, and crosses with the X B-2(1) at a similar angle. Therefore, if O-3(-) is produced in a highly bent geometry, B-2(2) might be preferentially populated. The large transition dipole moment and the vertical excitation energy for B-2(2)-->(2)A(1) also suggest that B-2(2) may be electronically excited efficiently to (2)A(1) at the wavelength of 523 nm. The computed energetics of B-2(2) and B-2(1) and the corresponding dissociation limits may explain the larger maximum kinetic energy release (KER) observed in the second experiment of Continetti and the smaller O-2-O- bond energy derived from the experiment of Hiller, if we assume that B-2(2) is the parent state in both cases. Furthermore, meta-IRC (intrinsic reaction coordinate) calculations suggest rather different final state distribution of the photofragments from B-2(1)-->(2)A(2) and B-2(2)-->(2)A(1) processes, in qualitative agreement with the experimental observations. Although the vibrationally excited ground state O-3(-) might also produce rotational hot, vibrational cold photofragments through the angular dependence of the seam between the two diabatic excited (2)A " states, the exact effect of parent vibrational excitation requires future dynamics calculations. At the current stage, our calculations strongly support that the B-2(2) electronic state has been accessed in the second experiment of Continetti et al.
Keywords:CONFIGURATION-INTERACTION CALCULATIONS;MOLECULAR-ORBITAL METHODS;SELF-CONSISTENT-FIELD;BASIS-SETS;WAVE-FUNCTIONS;ENERGY;ATOMS;SURFACES;EXCHANGE;NM