SPIN-ORBIT EFFECTS IN THE PHOTODISSOCIATION OF IONIZED RARE-GAS TRIMERS - COMPARISON OF HE-3(+), AR-3(+), AND XE-3(+)

The velocities of neutral and charged photofragments of the rare gas trimers He-3(+), Ar-3(+), and Xe-3(+) have been examined in a comprehensive study for photon energies ranging from 1.5 to 6 eV. For this purpose, a novel time-of-flight technique has been applied which allows the simultaneous examination of both neutral and charged fragments. The general fragmentation pattern of all three species was that of a linear trimer with a parallel transition moment and a totally repulsive excited state: In the course of the dissociation, two of the particles gain high velocities in opposite directions, while the third particle (the middle particle of the linear trimer) only obtains a small velocity The positive charge generally localizes on one of the fast outer particles, as can be expected from the symmetry properties of the excited state. For Ar-3(+) and Xe-3(+), however, also localization of the charge on the slow particle can be observed. This effect strongly depends on the energy of the absorbed photon, and can be quenched by decreasing the vibrational excitation of the trimer. Comparison of the results with new potential energy surface calculations indicate that mainly spin-orbit coupling induced conical intersections are responsible for this charge redistribution phenomenon. (C) 1995 American Institute of Physics.