Photoelectron imaging study of the effect of monohydration on O2- photodetachment

The photodetachment of the O2-center dot H2O cluster anion at 780 and 390 nm is investigated in comparison with O-2(-) 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-center dot H2O angular distributions are quantitatively similar to those for bare O-2(-). This observation confirms that the excess electron in O2-center dot H2O retains the overall character of the 2p pi(g)* HOMO of O-2(-). 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-center dot H2O exhibits a faster rise in the photodetachment signal with increasing eKE, as compared to O-2(-). The possible causes of this anomaly are (i) the long-range charge-dipole interaction between the departing electron and the neutral O-2(-), H2O skeleton affecting the slow-electron dynamics; and (ii) the s wave contributions to the photodetachment, which are dipole-forbidden for pi(-1)(g) transitions in O-2(-), but formally allowed in O2-center dot H2O due to lower symmetry of the cluster anion and the corresponding HOMO.