Infrared Spectroscopy of Jet-cooled Cationic Polyaromatic Hydrocarbons: Naphthalene[TSUP]+[/TSUP]

Abstract

The authors present the IR absorption spectrum of the jet-cooled naphthalene-Ar van der Waals cluster cation in the 400-1600 cm-1 range, which is expected to resemble closely the IR spectrum of the bare naphthalene cation. Cluster cations are produced in their ground states via resonance-enhanced 2-color ionization. Subsequent irradn. of the ions with IR light of a free-electron laser causes cluster dissocn., if this light is resonant with IR-active transitions of the cationic cluster. Mass-selective measurement of the dissocd. fraction as a function of IR wavelength yields the IR spectrum of the cationic cluster. Comparison with previously reported Ar matrix isolation spectra of naphthalene+ shows good agreement, with more bands obsd. The IR spectrum obsd. is compared to a calcd. spectrum of the naphthalene cation, allowing for unambiguous assignments of all the obsd. modes. The exptl. method presented is generally applicable to obtain lab. IR spectra of ionized polyarom. hydrocarbons under astrophys. relevant conditions. [on SciFinder(R)]