STUDY OF IN2P/IN2P- AND INP2/INP2- USING NEGATIVE-ION ZERO ELECTRON KINETIC-ENERGY SPECTROSCOPY

The zero electron kinetic energy (ZEKE) spectra of In2P- and InP2- are presented and compared to their previously obtained photoelectron spectra (PES) as well as ab initio calculations on analogous species. The threshold spectra, which give high-accuracy electron affinities of 2.400 +/- 0.001 eV for In2P and 1.617 +/- 0.001 eV for InP2, show well-resolved vibrational structure in the transitions from the ground anion states to the various neutral states. The ZEKE spectrum of In2P- exhibits a fairly extended, 47 cm(-1) progression that we assign to the symmetric bend (upsilon(2)) in the ground B-2(1) neutral state. There is also a 204 cm(-1) progression that we assign to the symmetric stretch. The InP2- ZEKE spectrum shows transitions to two electronic states of the neutral. For the ground state, the symmetric stretch mode is the most active in the spectrum, whereas in the excited state, the symmetric bend mode is most active. The InP2 ground-slate symmetric stretch frequency is 190 cm(-1), and the excited-state symmetric bend frequency is 287 cm(-1). An anion ground-state frequency is determined to be 227 cm(-1). The term energy of the excited state is determined to be 1.280 +/- 0.001 eV. Based on molecular orbital arguments, these frequencies suggest a B-2(2) ground InP2 state, a (2)A(1) first excited state, and a (1)A(1) anion ground state.