Spectroscopy and photophysics of 1Πg and 3Πg Rydberg, ion-pair states of Cl2, revealed by multiphoton ionization

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Abstract
Mass-resolved, two-photon resonant, three-photon ionization of jet-cooled Cl2 has been used to study the spectroscopy and photophysics of the lowest energy, double-well 1Πg and 3Πg states of mixed Rydberg (4sσ) and ion-pair character. Inner well levels from v′=0 (64 027 cm−1) to v′=15 (73 343 cm−1) have been observed for 1Πg of the mass 70 molecular chlorine isotope. Inner well levels for 3Πg have been observed from v′=0 at 63 472 cm−1 to the top of the barrier, and well beyond that to levels spanning both wells. Observation of these long progressions is attributed to excitation via a repulsive continuum at a well-phonon level. The photophysics of this latter process as well as the mechanism for copious atomic ion formation are discussed. Variation of linewidth with vibrational quantum number due to the predissociation of inner well levels is observed and attributed to repulsive valence states. The data are in good agreement with the theoretical calculations of Peyerimhoff and Buenker, and Tuckett and Peyerimhoff.