Dissociation dynamics of ion-pair states of Cl2 at principal quantum numbers beyond 1500

Long-lived ion-pair states of Cl2 have been observed by delayed pulsed-field ionization in the vicinity of the Cl-(1S0)+Cl+(3P2) dissociation threshold following single-photon excitation from the X 1Σg+(v=0) ground state with a tunable vacuum-ultraviolet laser. The field-ionization spectra reveal a series of resonances corresponding to ion-pair states with effective principal quantum number n* between 1858 and 1876 belonging to a series converging to the Cl-(1S0)+Cl+(3P0) dissociation threshold. These states are observed by forced predissociation into the Cl-(1S0)+Cl+(3P2) ion-pair channel. This process is the ion-pair analog of the process of forced autoionization observed in Rydberg states. The analysis of the spectra and of the field-ionization behavior provides information on the couplings between the relevant ionization and dissociation channels and has enabled the determination of the ion-pair dissociation threshold [EIPD(Cl-(1S0)+Cl+(3P2))=95 449.8±1.0 cm-1] and of the dissociation energies of Cl2 [D0(X 1Σg+)=19 998.4±1.1 cm-1] and Cl2+ [D0(X+2Πu)=31 942.1±1.5 cm-1].