Abstract
The photochemistry of glycolaldehyde (GA) upon irradiation at 266 nm is investigated in argon, nitrogen, neon, and para-hydrogen matrices by IR spectroscopy. Isomerization and fragmentation processes are found to compete. The hydrogen-bonded Cis-Cis form of GA is transformed mainly to the open Trans-Trans conformer and to CO and CH3OH fragments and their mixed complexes. Different photo-induced behaviours appear depending on the matrix. In nitrogen, small amounts of Trans-Gauche and Trans-Trans conformers are detected after deposition and grow together upon irradiation. The Trans-Gauche conformer is characterized for the first time. In para-hydrogen due to a weaker cage effect additional H2CO and HCO fragments are seen. Calculations of the potential energy surfaces of S0, S1, and T1 states--to analyse the torsional deformations which are involved in the isomerization process--and a kinetic analysis are presented to investigate the different relaxation pathways of GA. Fragmentation of GA under UV irradiation through the CO+CH3OH molecular channel is a minor process, as in the gas phase.
Highlights
Because they are widely present in the atmosphere, the fate of carbonyl compounds upon ultraviolet radiation has attracted numerous studies.1 When subject to electronic excitation, carbonyl compounds can dissociate to highly reactive species and undergo many cascade reactions by combining to radicals
They are compared to gas phase values14 and theoretical calculations
The TG conformer absorbs in this region (395 kJ/mol, 303 nm)
Summary
Because they are widely present in the atmosphere, the fate of carbonyl compounds upon ultraviolet radiation has attracted numerous studies. When subject to electronic excitation, carbonyl compounds can dissociate to highly reactive species and undergo many cascade reactions by combining to radicals. Because they are widely present in the atmosphere, the fate of carbonyl compounds upon ultraviolet radiation has attracted numerous studies.. When subject to electronic excitation, carbonyl compounds can dissociate to highly reactive species and undergo many cascade reactions by combining to radicals. Its photochemistry in the gas phase was extensively studied. It is only recently that the UV photolysis of pure GA in the gas phase was studied.. Photolysis end-products are similar to those previously observed in air except that CO2 is missing and intermediate products, i.e., hydroxyl (OH) and formyl (HCO) radicals were detected using cavity ring down spectroscopy. Four channels were considered in these previous works as first steps of photodissociation, of which three involve the formation of radicals: HOCH2COH + hν → HCO + CH2OH,
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