Gas-Phase Electronic Transitions of C17H12N+ at 15 K

The electronic spectrum of C17H12N+, phenanthrene with a side chain, was measured in the gas phase at a vibrational and rotational temperature of ∼15 K in an ion trap using a resonant multiphoton dissociation technique. The C17H12N+ structure was produced in a chemical ionization source and identified by a comparison with theoretical calculations of stable structures and excitation energies. The (3), (2), (1) 1A ← X 1A electronic transitions of this nitrogen-containing aromatic species with 30 atoms have origin band maxima at 23 586 ± 1 cm–1, 16 120 ± 50 cm–1, and 14 519 ± 30 cm–1. Distinct vibrational structure in the (3) 1A state is observed, and assignments are made. Astronomical aspects are considered.