Dissociation dynamics of ion-pair states of Cl2at principal quantum numbers beyond 1500

Abstract

Long-lived ion-pair states of Cl{sub 2} have been observed by delayed pulsed-field ionization in the vicinity of the Cl{sup -}({sup 1}S{sub 0})+Cl{sup +}({sup 3}P{sub 2}) dissociation threshold following single-photon excitation from the X {sup 1}{Sigma}{sub g}{sup +}(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{sup -}({sup 1}S{sub 0})+Cl{sup +}({sup 3}P{sub 0}) dissociation threshold. These states are observed by forced predissociation into the Cl{sup -}({sup 1}S{sub 0})+Cl{sup +}({sup 3}P{sub 2}) 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 [E{sub IPD}(Cl{sup -}({sup 1}S{sub 0})+Cl{sup +}({sup 3}P{sub 2}))=95 449.8{+-}1.0 cm{sup -1}] and of the dissociation energies of Cl{sub 2} [D{sub 0}(X {sup 1}{Sigma}{sub g}{sup +})=19 998.4{+-}1.1 cm{sup -1}] and Cl{sub 2}{sup +} [D{sub 0}(X{sup +} {sup 2}{Pi}{sub u})=31 942.1{+-}1.5 cm{sup -1}].