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

The threshold photodetachment zero-electron kinetic energy (ZEKE) spec trum of Si-3(-) is presented and discussed. The spectrum shows well-re solved vibrational structure. A comparison with several ab initio calc ulations 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' frequen cies 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 spect rum suggests that the negative ion is a fluxional, Jahn-Teller distort ed 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 c lose in energy, but that transitions to the singlet state are very wea k in the ZEKE spectrum.