Infrared spectra of 3-hydroxy-(1H)-pyridinium cation and 3-hydroxy-(1H)-pyridinyl radical isolated in solid para-hydrogen.

Abstract

As pyridine and its derivatives are regarded as building blocks of nitrogen-containing polycyclic aromatic hydrocarbons, spectral identifications of their protonated and hydrogenated species are important. The infrared (IR) absorption spectra of the 3-hydroxy-(1H)-pyridinium cation, 3-C5H4(OH)NH+, and the 3-hydroxy-(1H)-pyridinyl radical, 3-C5H4(OH)NH, produced on electron bombardment during deposition of a mixture of 3-hydroxypyridine, 3-C5H4(OH)N, and para-H2 to form a matrix at 3.2 K were recorded. Intense IR absorption lines of trans-3-C5H4(OH)NH+ at 3594.4, 3380.0, 1610.6, 1562.2, 1319.4, 1193.8, 1167.5, and 780.4 cm-1 and eleven weaker ones decreased in intensity after the matrix was maintained in darkness for 20 h, whereas lines of trans-3-C5H4(OH)NH at 3646.2, 3493.4, 3488.7, 1546.7, 1349.6, 1244.1, 1209.1, 1177.3, 979.8, and 685.2 cm-1 and nine weaker ones increased. The intensities of lines of trans-3-C5H4(OH)NH decreased upon irradiation at 520 nm and diminished nearly completely upon irradiation at 450 nm, whereas those of trans-3-C5H4(OH)NH+ remained unchanged upon irradiation at 370, 450, and 520 nm. Observed vibrational wavenumbers and relative intensities of these species agree satisfactorily with the scaled harmonic vibrational wavenumbers and IR intensities predicted with the B3LYP/aug-cc-pVTZ method. The observed 3-C5H4(OH)NH+ cation and 3-C5H4(OH)NH radical are predicted to be the most stable species among all possible isomers by quantum-chemical calculations.