10min:

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

Lanthanum dimer (La₂) was studied by mass-analyzed threshold ionization (MATI) spectroscopy and a series of high-level multi-configuration ab initio calculations (CASSCF, CASPT2, and MRCI). The MATI spectrum exhibits three band systems originating at 39044, 40312, and 40862 cm^-1, respectively. Above the band origin, the first band system displays a vibrational progression of 232 cm^-1, and the other two show vibrational progression with the same interval of 240 cm^-1. Below the band origin, the three systems exhibit the same vibrational interval of 207 cm^-1. These band systems are assigned to three electronic transitions from the ground state of La₂ to the low-lying electronic states of La₂⁺: ^{2 +}_g ^{1 +}_g, ² _u,1/2 ^{1 +}_g, and ² _u,3/2 ^{1 +}_g. The spin-orbit splitting in the ² _u ion state is 550 cm^-1. In addition, the electronic states and bonding of La₂ will be compared with those of Sc₂ and Y₂.