Gas-phase infrared spectra of cationized nitrogen-substituted polycyclic aromatic hydrocarbons

• Published in: Astronomy and astrophysics (Berlin) 2010-07, Vol.517, p.A15
• Main Authors: Alvaro Galué, H., Pirali, O., Oomens, J.
• Format: Article
• Language: English
• Subjects: astrochemistry; ISM: molecules; methods: laboratory; molecular processes; techniques: spectroscopic
• ISSN: 0004-6361; 1432-0746
• DOI: 10.1051/0004-6361/201014050

Gas-phase infrared spectra of several ionized nitrogen substituted polycyclic aromatic hydrocarbons (PANHs) have been recorded in the 600–1600 cm-1 region via IR multiple-photon dissociation (IRMPD) spectroscopy. The UV photoionized PANH ions are trapped and isolated in a quadrupole ion trap where they are irradiated with an IR free electron laser. The PANHs were studied in their radical cation (PANH+) and protonated (H+PANH) forms, and include quinoline, isoquinoline, phenanthridine, benzo[h]quinoline, acridine, and dibenzo[f,h]quinoline. Experimental IRMPD spectra were interpreted with the aid of density functional theory methods. The PANH+ IR spectra are found to resemble those of their respective non-nitrogenated PAH cations. The IR spectra of H+PANHs are significantly different owing to the NH inplane bending vibration, which generally couples very well with the aromatic CH bending and CC stretching modes. Implications of the NPAH (+, H+) laboratory spectra are discussed for the astrophysical IR emissions and, in particular, for the band at 6.2 μm.