Photoelectron Imaging Study of the Effect of Monohydration on O2- Photodetachment

The photodetachment of the O2-âH2O cluster anion at 780 and 390 nm is investigated in comparison with O2- using photoelectron imaging spectroscopy. Despite the pronounced shift in the photoelectron spectra, the monohydration has little effect on the photoelectron angular distributions: for a given wavelength and electron kinetic energy (eKE) range, the O2-âH2O angular distributions are quantitatively similar to those for bare O2-. This observation confirms that the excess electron in O2-âH2O retains the overall character of the 2pðg* HOMO of O2-. The presence of H2O does not affect significantly the partial wave composition of the photodetached electrons at a given eKE. An exception is observed for slow electrons, where O2-âH2O exhibits a faster rise in the photodetachment signal with increasing eKE, as compared to O2-. The possible causes of this anomaly are (i) the long-range charge-dipole interaction between the departing electron and the neutral O2âH2O skeleton affecting the slow-electron dynamics; and (ii) the s wave contributions to the photodetachment, which are dipole-forbidden for ðg-1 transitions in O2-, but formally allowed in O2-âH2O due to lower symmetry of the cluster anion and the corresponding HOMO. 1