Electronic absorption spectrum of cold naphthalene cation in the gas phaseby photodissociation of its van der Waals complexes

The electronic absorption spectrum of the naphthalene cation has been obtai ned in conditions relevant for comparison with the diffuse interstellar ban ds in astrophysics, i.e., cold species in the gas phase. The novel techniqu e consisting to photodissociate a selectively R2P2CI-prepared PAH-argon van der Waals complex in a molecular beam [Ph. Brechignac and T. Pino, Astron. Astrophys. 343, L49 (1999)] has been used. The various aspects of the meth od are described in detail. The whole visible range has been explored revea ling two electronic transitions displaying 28 vibronic bands. Absolute abso rption cross sections have also been measured, and found much larger than r eported from rare gas matrices studies. The additional information on the m atrix-induced or complex-induced shifts and widths, and on the intramolecul ar and intermolecular processes involved in these species, is discussed. No definite conclusion about the possible presence of the cation in space can be drawn so far. (C) 1999 American Institute of Physics. [S0021-9606(99)00 740-0].