15min:

LU WU, CHANGHUA ZHANG, SERGIY KRASNOKUTSKI AND DONG-SHENG YANG, Department of Chemistry, University of Kentucky, Lexington, KY 40506-0055.

Lanthanum oxide clusters are produced by laser vaporization in a pulsed 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 La₂O₂ and La₃O₄ exhibit a very strong 0-0 transition, indicating similar geometries for the neutral and ionized clusters and a very weakly bonding or non-bonding electron ejected from an outmost molecular orbital. The ionization energies of La₂O₂ and La₃O₄ are measured to be 36937(5) and 28028(5) cm^-1, respectively. In addition, the spectra of both clusters display a number of vibrational intervals that are associated with metal-metal, metal-oxygen, and oxygen-oxygen vibrations. Preliminary data analysis shows that the La₂O₂ cluster has a D_2h planar structure and La₃O₄ has a C_3v cage-like structure, both with alternating La-O-La bonds. The spectra may be assigned to the ²Ag ¹Ag transition in the case of La₂O₂ and ¹A₁ ²A₁ in La₃O₄ .