| Abstract
| - Picolinamide (PA) and isonicotinamide (INA), two structural isomers of pyridinecarboxamide, have beeninvestigated by matrix isolation and low-temperature solid-state infrared spectroscopy, combined with UV (λ> 235 nm) photoexcitation and density functional theory and ab initio (MP2) theoretical studies. In consonancewith the theoretical data, both PA and INA were found to exist in a single conformation in cryogenic rare gasmatrixes. Comparison between the experimental spectra of the matrix-isolated compounds with thosetheoretically predicted allowed for full assignment of the experimental spectra. In situ UV (λ > 235 nm)irradiation of the matrixes showed that only PA reacts, with production of isocyanic acid and pyridine, thefirst photoproduct further reacting to yield CO + NH and cyanic acid. The different photochemical behaviorof the two compounds was explained taking into consideration their different structures. The infrared spectraof (i) the low-temperature glassy state resulting from fast deposition of vapors of the compounds onto asubstrate cooled to 10 K, (ii) the crystal resulting from the annealed amorphous film of the compound, and(iii) the room-temperature crystals (α-phase) of the studied compounds were also obtained, fully assignedand correlated with intermolecular interactions present in the condensed phases, in particular H-bondinteractions, showing that these latter are stronger in INA than in PA.
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