| Abstract
| - We report a deperturbation analysis of the[18.5]1-X0+ system of ReN. HeterogeneousJa uncoupling involvinga “dark” (Ω = 2) state is responsible for the observedperturbation. For the (0−0) band located near 540nm,extra branches as well as an irregular energy level pattern areobserved. For the (1−0) band near 510 nm,although the observed spectrum appears regular, the B‘ value deducedfrom a previous analysis is not consistentwith values associated with other vibrational levels. A carefulreexamination of this band, using dispersedfluorescence to filter the laser induced fluorescence (LIF) spectra,allowed us to separate the “bright” and“dark” state contributions to the original LIF spectrum. Infact two spectra can be obtained, correspondingmainly either to the “bright” or to the “dark” excited states.Rotational analyses have been carried out forboth of these (1−0) bands and confirm the deperturbation analysis ofthe (0−0) bands. Excited state lifetimeshave been measured for individual ro-vibrational levels of the“bright” state. These lifetimes exhibit a largevariation with rotational and vibrational quanta, an effect consistentwith the proposed heterogeneous uncouplingmechanism. Dispersed fluorescence spectra have been recorded forall previously observed excited states.These spectra reveal the presence of a number of new low-lyingstates and the analysis helps to establishtheir Ω values. The current observations are consistent with thepreviously proposed electronic structure.However, the Franck−Condon factors inferred from the presentstudy suggest that strong interactions existamong many of the excited states.
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