Three new ionhyphen;pair states of molecular chlorine have been identified by the double resonance method utilizing a sequential threehyphen;photon absorption. Two independently tunable dye lasers were used to excite the chlorine molecules into a specific rovibronic level of theBthinsp;3Pgr;0+ustate, and subsequently into levels ofungeradeexcited states by a simultaneous twohyphen;photon transition. The method enabled us to observe transitions to the low vibrational levels of ionhyphen;pair states in the energy range of 7.3ndash;7.7 eV, which were directly inaccessible from the ground state due to the small Franckndash;Condon factors. Their spectroscopic parameters were derived from the vibrational and rotational analyses of two separate isotope species,35Clndash;35Cl and35Clndash;37Cl. The twohyphen;photon transitions from theB3Pgr;0+ustate to ionhyphen;pair ones consisted of simpleO,Q, andSbranches. The polarization effect on their transition probability established that the symmetry of three ionhyphen;pair states was 0+uin the Hundrsquo;s casecnotation. The properties of these ionhyphen;pair states are discussed in terms of the electron configuration.
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