Infrared Spectra of 1-Quinolinium (C 9 H 7 NH + ) Cation and Quinolinyl Radicals (C 9 H 7 NH and 3-, 4-, 7-, and 8-HC 9 H 7 N) Isolated in Solid para- Hydrogen.

Large protonated polycyclic aromatic hydrocarbons (H + PAH) and the corresponding nitrogen heterocycles (H + PANH) have been proposed as possible carriers of unidentified infrared (UIR) emission bands from galactic objects. The nitrogen atom in H + PANH is expected to induce a blue shift of the band associated with the CC-stretching mode of H + PAH near 6.3 μm so that their emission bands might agree better with the UIR band near 6.2 μm. We report the IR spectrum of protonated quinoline (1-quinolinium cation, C 9 H 7 NH + ) and its neutral species (1-quinolinyl radical, C 9 H 7 NH) measured upon electron bombardment during the deposition of a mixture of quinoline (C 9 H 7 N) and para -hydrogen ( p -H 2 ) at 3.2 K, indicating that the protonation and hydrogenation occur mainly at the N atom site. Additional experiments on the irradiation of C 9 H 7 N/Cl 2 / p -H 2 matrices at 365 nm to generate Cl atoms, followed by irradiation with IR light to generate H atoms via Cl + H 2 ( v = 1), were performed to induce the reaction H + C 9 H 7 N. This method proved to be efficient for hydrogenation reactions in solid p -H 2 ; we identified, in addition to C 9 H 7 NH observed in electron-bombardment experiments, four radicals with hydrogenation at the C-atom site─3-, 4-, 7-, and 8-HC 9 H 7 N. Spectral assignments were achieved according to the behavior upon secondary photolysis and a comparison of experimental results with vibrational wavenumbers and IR intensities predicted with the B3LYP/6-311++G(d,p) method. The observed lines at 1641.4, 1598.4, and 1562.0 cm -1 associated with the CC-stretching mode of C 9 H 7 NH + are blue-shifted from those at 1618.7, 1580.8, 1556.7, and 1510.0 cm -1 of the corresponding protonated naphthalene (C 10 H 9 + ).