B-X and C-X Band Systems of CuCl Revisited: Laser-induced Fluorescence Study in 465−490 nm

We have reinvestigated the B-X and C-X band systems of CuCl by recording the laser-induced fluorescence excitation spectra in 20400?21800 cm^?1. The rotational analyses in Hund’s case (a) revealed unambiguously a singlet-to-singlet transition nature. The radiative lifetimes were measured to be 4.670 and 4.667 μs, respectively, which are much longer than that expected for a pure singlet of CuCl. This implies that the fluorescence mechanism in the B or C band systems lies in the mixing of the singlets (¹Пand ¹∑⁺) and triplets (³П_0,1,2) and that the two excited states observed in our experiment might be the singlets that have been strongly “contaminated” by their triplet neighbors.