Hydrocarboxyl Radical as a Product of α‑Alanine Ultraviolet Photolysis

• Published in: The journal of physical chemistry letters Vol. 12; no. 50; pp. 11992 - 11997
• Main Authors: Moore, Brendan, Toh, Shin Yi, Wong, Y. T. Angel, Bashiri, Termeh, McKinnon, Alexandra, Wai, Yonnie, Alethea Lee, Ka Wing, Ovchinnikov, Polina, Chiang, Chih-Yu, Djuricanin, Pavle, Momose, Takamasa
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 23-12-2021
• Subjects: Alanine - chemistry; Carbon Dioxide - chemistry; Isomerism; Photolysis - radiation effects; Physical Insights into Light Interacting with Matter; Quantum Theory; Ultraviolet Rays
• ISSN: 1948-7185; 1948-7185
• DOI: 10.1021/acs.jpclett.1c03104

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.