			15min:

MASS-ANALYZED THRESHOLD IONIZATION AND STRUCTURES OF M₃C₂(M=Sc, La).

LU WU, ROUDJANE MOURAD AND D. S. YANG, Department of Chemistry, University of Kentucky, Lexington, KY 40506-0055.

M₃C₂ (M=Sc, La) clusters are produced by laser vaporization in a pulsed metal-cluster source and identified by photoionization mass spectrometry. Vibrationally resolved ion spectra are obtained with mass-analyzed threshold ionization (MATI) spectroscopy. The MATI spectra of M₃C₂ (M=Sc, La) exhibit a weak 0-0 transition, indicating a significant geometry difference between the neutral and ionized clusters. The ionization energies of Sc₂C₂ and La₃C₂ are measured to be 36398 (5) and 30051(5) cm^-1, respectively. In addition, the spectra of the two clusters display a number of vibrational intervals that are associated with M₃ deformations. Preliminary data analysis shows that both clusters have a C_2v bi-pyramid structure in the neutral state and a D_3h bi-pyramid structure in the ion state, and the spectra may be assigned to the ¹A'₁ (D_3h) leftarrow ²B₂ (C_2v) transitions.