Molecular ions and electron transport in rare gas lattices: C−2 formation mechanism and X 2Σ+g↔B 2Σ+u spectroscopy

Tunable laser excitation of the C−2 B 2Σ+u →X 2Σ+g emission spectrum in rare gas lattices uncovers a strong Personov effect—narrowing in emission of an inhomogeneously broadened absorption spectrum. Single site emission spectra show moderate coupling with delocalized lattice phonons, and the zero phonon ’’quasiline’’ broadens and shifts red as a function of increasing temperature. The solid phase spectroscopic constants suggest that C−2 is a substitutional guest in Ar, Kr, and Xe, while displacing two or more atoms in Ne. The formation of C−2 in 1216 Å photolyzed, acetylene doped rare gas solids can be understood in terms of single photon ionization schemes in dielectric media. A long range (10–20 Å) electron tunneling from the C−2 excited B state in Ne to a nearby cation is observed with rate constant ?103 sec−1. A general classification of ion pairs in dielectric media as either ’’coulomb’’ or ’’chemically bonded’’ is proposed.