title: Infrared spectra of the 1-pyridinium (C5H5NH+) cation and pyridinyl (C5H5NH and 4-C5H6N) radicals isolated in solid para-hydrogen.
abstract: Protonated pyridine and its neutral counterparts (C5H6N) are important intermediates in organic and biological reactions and in the atmosphere. We have recorded the IR absorption spectra of the 1-pyridinium (C5H5NH(+)) cation, 1-pyridinyl (C5H5NH), and 4-pyridinyl (4-C5H6N) produced on electron bombardment during matrix deposition of a mixture of pyridine (C5H5N) and p-H2 at 3.2 K; all spectra were previously unreported. The IR features of C5H5NH(+) diminished in intensity after the matrix was maintained in darkness for 15 h, whereas those of C5H5NH and 4-C5H6N radicals increased. Irradiation of this matrix with light at 365 nm diminished lines of C5H5NH(+) and C5H5NH but enhanced lines of 4-C5H6N slightly, whereas irradiation at 405 nm diminished lines of 4-C5H6N significantly. Observed wavenumbers and relative intensities of these species agree satisfactorily with the anharmonic vibrational wavenumbers and IR intensities predicted with the B3LYP/6-31++G(d,p) method. Assignments of C5H5NH and 4-C5H6N radicals were further supported by the observation of similar spectra when a Cl2/C5H5N/p-H2 matrix was irradiated first at 365 nm and then with IR light to generate H atoms to induce the H + C5H5N reaction.
authors.affiliation: Department of Applied Chemistry and Institute of Molecular Science, National Chiao Tung University , Hsinchu 30010, Taiwan.
authors.forename: Barbara
authors.initials: B
authors.lastname: Golec
authors.forename: Prasanta
authors.initials: P
authors.lastname: Das
authors.forename: Mohammed
authors.initials: M
authors.lastname: Bahou
authors.forename: Yuan-Pern
authors.initials: YP
authors.lastname: Lee
mesh_terms: D004583:Electrons; D006859:Hydrogen / Q000737:chemistry*; D008958:Models, Molecular; D008968:Molecular Conformation; D010782:Photolysis; D011725:Pyridines / Q000737:chemistry*; D011726:Pyridinium Compounds / Q000737:chemistry*; D011789:Quantum Theory; D013055:Spectrophotometry, Infrared
chemical_list: D011725:Pyridines; D011726:Pyridinium Compounds; D006859:Hydrogen; C023666:pyridine