ABSORPTION-SPECTROSCOPY AND PHOTODISSOCIATION DYNAMICS OF SMALL HELIUM CLUSTER IONS

The optical absorption of size-selected helium cluster ions was studied via photofragmentation spectroscopy. Absorption cross sections were measured for Hen+ (n=3, 4, 10, 21, and 30). A broad absorption peak was found, which for He3+ is centered at ≈5.3 eV, and which with increasing cluster size shifts slightly to the red. In addition, the kinetic energy release to the ionized and neutral photofragments was measured by a time-of-flight technique for cluster sizes between n=3 and 10. From the energy balance the total binding energy of the He3+ trimer ion was determined to be 2.6±0.15 eV. The results further indicate that a charged linear trimer acts as a core molecule for the sizes n=4-7. For n>7, an additional isomer with a tetramer core is identified. The results are compared with recent ab initio calculations. © 1995 American Institute of Physics.