MASS-ANALYZED THRESHOLD IONIZATION AND STRUCTURES OF M$_3$C$_2$(M=Sc, La)

Abstract

M$_3$C$_2$ (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 M$_3$C$_2$ (M=Sc, La) exhibit a weak 0-0 transition, indicating a significant geometry difference between the neutral and ionized clusters. The ionization energies of Sc$_2$C$_2$ and La$_3$C$_2$ 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 M$_3$ 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$_{3h}$)$\leftarrow$ $^2B_2$ (C$_{2v}$) transitions.