THRESHOLD PHOTODETACHMENT ZERO-ELECTRON KINETIC-ENERGY SPECTROSCOPY OF SI-3(-)

The threshold photodetachment zero-electron kinetic energy (ZEKE) spectrum of Si-3(-) is presented and discussed. The spectrum shows well-resolved vibrational structure. A comparison with several ab initio calculations shows that the spectrum is due to transitions to the (3)A(2)' (D-3h) state of Si-3. The symmetric stretch and degenerate e' frequencies for the Si-3 (3)A(2)' State are determined to be 501+/-10 and 337+/-10 cm(-1), respectively. Additional structure observed in the spectrum suggests that the negative ion is a fluxional, Jahn-Teller distorted species; The ZEKE spectrum shows no evidence for transitions to the (1)A(1) state of the neutral, which is predicted to lie very close to the (3)A(2)' state. A comparison of the ZEKE and previously obtained photoelectron spectrum of Si-3(-) suggests that these two states are close in energy, but that transitions to the singlet state are very weak in the ZEKE spectrum.