Electric-field-enhanced laser-induced plasma spectroscopy of jet-cooled silicon trimer

Electric-field-enhanced laser-induced plasma spectroscopy is used as a relatively simple and general approach to a mapping of electronic states and internal mode structure in small silicon clusters, primarily silicon trimer. Gas phase emission spectra obtained for the trimer correlate well with and extend data obtained in gas phase negative ion photoelectron spectroscopy and in matrix isolation absorption spectroscopy. Transitions are observed from an upper state, the analog of that observed in matrix absorption to both the ground (X) and low-lying A state (0.45 eV). The observed emission from the two band systems suggests that the features are associated primarily with short progressions in upper (≈310±25 cm −1 ) and lower state (≈370±25 cm −1 for X state and ≈ 480±25 cm −1 for A state) symmetric stretch or symmetric strench—bend combination frequencies. Some indication of upper and lower state bending mode structure is also obtained. Comparisons are made with ab initio calculations.