Photochemical Study and Vibrational Spectra of Propiolamide Isolated in Low-Temperature Ar, Xe, and N2 Matrices

Propiolamide (HC---CCONH2, PA) has been isolated in low-temperature matrices (Ar, Xe, and N2) and studied by matrix isolation infrared (IR) spectroscopy and quantum chemical calculations undertaken at the DFT(B3LYP)/6-311++G(d,p) level of theory. In situ broadband UV light (lambda > 235 nm) irradiation of matrix-isolated PA led to the observation of new bands ascribed to different photoproducts resulting from three distinct photoreaction pathways: (i) tautomerization to propiolimidic acid (HC---CC(OH)--NH), (ii) C-C bond cleavage, with forma -tion of acetylene (HC---CH) and isocyanic acid (HNCO), and (iii) decarbonylation, leading to generation of ethynamine (HC---CNH2). Pathways (i) and (ii) were observed in all matrices, while (iii) was only observed in the matrices of the rare gases. Observation of characteristic bands due to the different photoproducts has been established, and the assignment of the IR spectra for all the species was carried out. As a whole, the detailed structural, vibrational, and photochemical data reported in this article appear relevant to the rational practical use of PA in its multiple application areas (in particular in the pharmaceutical and materials sciences domains) as well as for its analytical determination, including its search in the interstellar space.