Infrared Spectra of 1-Quinolinium (CHNH) Cation and Quinolinyl Radicals (CHNH and 3-, 4-, 7-, and 8-HCHN) Isolated in Solid Hydrogen.

Large protonated polycyclic aromatic hydrocarbons (HPAH) and the corresponding nitrogen heterocycles (HPANH) have been proposed as possible carriers of unidentified infrared (UIR) emission bands from galactic objects. The nitrogen atom in HPANH is expected to induce a blue shift of the band associated with the CC-stretching mode of HPAH 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, CHNH) and its neutral species (1-quinolinyl radical, CHNH) measured upon electron bombardment during the deposition of a mixture of quinoline (CHN) and -hydrogen (-H) at 3.2 K, indicating that the protonation and hydrogenation occur mainly at the N atom site. Additional experiments on the irradiation of CHN/Cl/-H matrices at 365 nm to generate Cl atoms, followed by irradiation with IR light to generate H atoms via Cl + H ( = 1), were performed to induce the reaction H + CHN. This method proved to be efficient for hydrogenation reactions in solid -H; we identified, in addition to CHNH observed in electron-bombardment experiments, four radicals with hydrogenation at the C-atom site─3-, 4-, 7-, and 8-HCHN. 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 associated with the CC-stretching mode of CHNH are blue-shifted from those at 1618.7, 1580.8, 1556.7, and 1510.0 cm of the corresponding protonated naphthalene (CH).