Three rare gas halide (RgX−) anions, ArBr−, ArI−, and KrI−, and the corresponding open-shell van der Waals complexes, ArBr, ArI, and KrI, were studied with anion zero electron kinetic energy (ZEKE) spectroscopy. Photodetachment of each anion accesses the three lowest-lying electronic states (the X1/2, I3/2, and II1/2 states) of the neutral complex. The spectra for each system reveal well-resolved progressions in the low frequency vibrations of the anion and the three neutral electronic states, providing a detailed spectroscopic probe of the Rg⋅X− and Rg⋅X interaction potentials. The line shapes observed in the ZEKE spectra are analyzed in terms of the line strengths of the underlying rotational transitions. From our data, we construct the potential energy curve for each neutral state as well as for the anion, and these interaction potentials are compared to potentials obtained from scattering and ion mobility experiments.

The threshold photodetachment (ZEKE) spectrum of Si-is presented. Although no transitions to the ground state of Si 4 are observed, we obtain detailed information on the anion and several of the low-lying excited states of neutral Si 4. The spectrum shows a long progression of wellresolved transitions between the D2h 2 B2g rhombus anion and v 2 vibrational levels of the first excited D 2 h 3 B 3 U neutral. The length and spacing of the progression is consistent with ab initio calculations performed by Rohlfing and Raghavachari [J. Chem. Phys. 96, 2114 (1992)], but some of the sequence bands observed within the progression are not. We also observe transitions to the Si 4 'B 3 , state which is found at a lower excitation energy than predicted. The perturbed vibrational structure in this band is attributed to vibronic coupling to a nearby electronic state which is "dark" with respect to ZEKE spectroscopy. The ZEKE spectra are compared to the previously obtained photoelectron spectra of Sias well as ab initio calculations on Si4-and Si 4 .

Small indium phosphide clusters having 2–8 atoms are studied using anion photoelectron spectroscopy of InxP−y (x,y=1–4). From these spectra, the electron affinities are determined. Both ground and low-lying excited electronic states of the neutral clusters are observed. An electronic gap is shown in the even cluster anion spectra.