Vibrational and rotational analyses of bands between 636 and 660Â nm in the red system of CuCl2

The long wavelength end of the electronic spectrum of CuCl2, between 636 and 660 nm, has been recorded in the gas phase by laser-excitation spectroscopy using a sample prepared at low temperatures (ca. 10 K) in a free-jet expansion. Under these conditions, it is possible to resolve vibrational, rotational, and even Cu hyperfine structure. The (0, 0) band of the E2Πu-X2Πg transition has been identified with an origin at 15546.286(3) cm−1 for 63Cu35Cl2. The observation and analysis of bands involving vibrationally excited levels has allowed the determination of all three vibrational intervals for the E2Πu state (ν1 = 335.88 cm−1, ν2 = 112.42 cm−1, and ν3 = 482.17 cm−1, 63Cu35Cl2). In addition, two other, unrelated transitions have been identified in the same narrow wavelength region. This, combined with the observation of local perturbations of the rotational structure in various bands, reveals the presence of other closely lying electronic states in the same energy region.