Vibrational spectroscopy of gas-phase neutral and cationic phenanthrene in their electronic groundstates

Various experimental methods are applied to retrieve the vibrational structure of phenanthrene in its neutral and cationic groundstates. The linear infrared (IR) absorption spectra in the 400–1650 cm−1 range of jet-cooled phenanthrene and its cation, both clustered with either an argon or a neon atom, are obtained via photo-induced cluster dissociation spectroscopy. The spectra observed are in good agreement with calculated spectra of the bare species. However, the observed spectrum of cationic phenanthrene shows more lines and lines with different intensities in the 900–1400 cm−1 range than expected from calculations. Additional spectra of the perdeuterated phenanthrene–Ar cation, and the warm (T≿room temperature) bare phenanthrene cation are recorded. Also the mass-analyzed threshold ionization spectra of bare phenanthrene and phenanthrene–Ar are recorded and compared with each other. Comparison of the spectral data recorded to calculated spectra of bare neutral, cationic and cationic perdeuterated phenanthrene, as well as to IR spectra recorded in matrix–isolation experiments, explicitly demonstrates that cluster dissociation spectroscopy is a valid and powerful method to obtain IR spectroscopic information of bare neutral and cationic jet-cooled poly-aromatic hydrocarbons