Hydrocarboxyl Radical as a Product of α-Alanine Ultraviolet Photolysis

UV photodissociation of α-alanine was studied by parahydrogen matrix isolation infrared spectroscopy. The temporal behavior of Fourier transform infrared spectra revealed that UV irradiation at 213 nm yielded the HOCO radical as a direct photoproduct from the S₂ excited state. The concentration of HOCO quickly approached a steady state due to secondary photodissociation of HOCO to produce CO₂ + H or CO + OH. On the other hand, no photoproducts were detected by S₁ excitation at 266 nm. Irradiation of fully deuterated α-alanine at 213 nm yielded ∼2 times more cis-DOCO radicals than the lower energy isomer trans-DOCO, indicating that the conformation of the hydroxyl group is fairly well-preserved upon photodissociation of α-alanine. The present study suggests that HOCO may be a good tracer species in the search for amino acids in interstellar space.