NEAR-INFRARED 2-PHOTON LASER SPECTROSCOPY OF THE 2 1-SIGMA-G+ STATE OF LI-7(2)

The results of a nonresonant near infrared two-photon laser spectroscopic study of the 2 1-SIGMA-g+ state of (Li2)-Li-7 are presented. Over 1000 rotationaly resolved 2 1-SIGMA-g+ <-- X 1-SIGMA-g+ transitions spanning 2300 cm-1 of the 2 1-SIGMA-g+ potential well have been assigned and analyzed. Data from the upsilon' = 1 to upsilon' = 21 vibrational levels are used to obtain 2 1-SIGMA-g+ state Dunham molecular constants as well as band-by-band constants. These data are also used to construct a Rydberg-Klein-Rees (RKR) potential which corresponds to 89% of the potential well depth. The results for the lower upsilon' levels are in agreement with the previously determined molecular constants for upsilon' = 0 to upsilon' = 16 [J. Mol. Spectrosc. 116, 271 (1986)]. For the higher upsilon' levels they reveal the perturbations from the 1 1-PI-g state. Comparisons with the results of ab initio calculations are made. In the 2 1-SIGMA-g+ <-- X 1-SIGMA-g+ nonresonant two-photon excitation only Q-branch transitions are observed with plane polarized radiation.