Transition state dynamics of OHF on several electronic states: photodetachment spectrum of OHF- and conical intersections.

Wave packet simulations of the photodetachment spectrum of OHF(-) are performed on several electronic adiabatic states, two triplets and four singlets of neutral OHF. The transition moments to these six states have been approximated using the ab initio electronic wave functions of OHF(-) and OHF calculated at the equilibrium configuration of the parent anion. In a first step, two-dimensional simulations of the spectrum are performed on new two-dimensional potential energy surfaces (PESs) of the neutral in a OHF collinear geometry. The resulting simulated spectrum is in rather good agreement with the experimental one, reproducing all the structures from 0 to 2.5 eV electron kinetic energies. At energies below 0.5 eV, all calculated states, singlets and triplets, contribute to the total spectrum. At higher energies, however, only the triplet states participate. In a second step, to improve the description of the spectrum, three-dimensional wave packet simulations of the spectrum are performed, getting an excellent agreement with the experiment. The collinear (3)Sigma(-) and (3)Pi states split in two (3)A(") and one (3)A('). New adiabatic PESs are used in this work for the 2 (3)A(") and 1 (3)A(') states, while the one recently proposed was used for the ground 1 (3)A("). It is found that the minimum energy paths of the (3)Sigma(-) and (3)Pi states cross twice at collinear geometry, so that at the transition state the ground state corresponds to (3)Pi, while (3)Sigma(-) is the lowest state otherwise. Such conical intersections are expected to give rise to important Sigma-Pi vibronic effects, requiring a complete three-dimensional model of coupled diabatic states to improve our understanding of the reaction dynamics in this kind of systems.