Observation of three weakly bound valence states of I2

Structured emission in the gas phase to two weakly bound valence states that correlate with the third dissociation limit, I-*(P-2(1/2))+I-*(P-2(1/2)), designated as (bb), from two third tier ion-pair states of I-2 correlating with I-(S-1(0))+I+(D-1(2)), the 1(g)(D-1(2)), and F(')0(u) (+)(D-1(2)) states, has been observed for the first time. The 1(u)(bb) state is shown to be bound by 377 +/- 2 cm(-1) and molecular constants have been determined. Vibrational structure in the 0(g)(+)(bb) state could not be resolved but the spectrum is consistent with the state being bound by 435 cm(-1). The relative integrated intensities of the emissions from both ion-pair states to various valence states have also been measured, and some aspects are rationalized in terms of the electronic configurations of the upper and lower states. Bound levels of a previously uncharacterized 1(g)(ab) valence state have also been observed in emission from the gamma 1(u)(P-3(2)) ion-pair state. The lower state is shown to be bound by 270 +/- 2 cm(-1) and molecular constants have been determined. (C) 2007 American Institute of Physics [DOI:10.1063/1.2795722]