STUDY OF THE LOW-LYING ELECTRONIC STATES OF SI-2 AND SI-2- USING NEGATIVE-ION PHOTODETACHMENT TECHNIQUES

The low-lying electronic states of Si2- and Si2 were studied using both photoelectron spectroscopy and threshold photodetachment spectroscopy of Si2-. Our measurements show that the ground state of Si2 is the X 3-SIGMA-g- state and that the X 3-SIGMA-g--D 3-PI-u splitting is 0.083 +/- 0.010 eV. Additional spectroscopic constants for the X 3-SIGMA-g-, D 3-PI-u, a 1-DELTA-g, b 1-PI-u and c 1-SIGMA-g+ states of Si2 were also determined. For Si2-, the first two electronic states were identified as: 2-PI-u (T(e) = O, r(e) = 2.207 +/- 0.005 angstrom, and v = 533 +/- 5 cm-1) and 2-SIGMA-g+ (T(e) = 0.025 +/- 0.010 eV, r(e) = 2.116 +/- 0.005 angstrom, and v = 528 +/- 10 cm-1). The electron affinity for Si2 was found to be 2.176 +/- 0.002 eV. Our results provide definitive orderings and splittings for the low-lying electronic states in both Si2 and Si2-.