15min:

N. P. ROEHR, J. SZCZEPANSKI, N. C. POLFER, Department of Chemistry, University of Florida, Gainesville, FL 32608.

Obtaining UV/Vis absorption spectra of cations is a challenging endeavor due to the low densities that can be achieved in the gas phase. In matrix isolation, ions of interest are accumulated in a cold inert matrix of a rare gas (e.g. Argon, Neon) until sufficient concentrations are attained for direct spectroscopic characterization . Nonetheless, in order to ensure neutralization of the matrix, experimentalists often rely on non-ideal, energetic processes, such as electron emission from metal surfaces upon cation bombardment . A better method for matrix neutralization would involve co-depositing a molecular counter-ion. In this talk, a two-ion source instrument is presented, where cations and anions are deposited into a cold inert matrix. Mass-selected cation beams are generated in an electron ionization source and filtered in a quadrupole mass filter (5-10 nA mass-selected naphthalene radical cations recorded). Anion beams are generated in a chemical ionization source (20 nA SF₆^- recorded). Both ion beams are introduced into an octopole ion guide via a quadrupole deflector. Cations and anions can be deposited simultaneously or separately; in the latter case, alternating layers of each species can be formed. Target cations of interest include open-shell naphthalene and tetracene, for which UV/Vis absorption spectra are recorded after deposition ^,. The counter-ion of choice is SF₆^-, due to the high electronegativity of SF₆.