Hydroxyl Radical Fluorescence and Quantum Yield Following Lyman‑α Photoexcitation of Water Vapor in a Room Temperature Cell and Cooled in a Supersonic Expansion

• Published in: The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory Molecules, spectroscopy, kinetics, environment, & general theory, 2018-06, Vol.122 (25), p.5602-5609
• Main Authors: Young, Justin W, Booth, Ryan S, Vogelhuber, Kristen M, Stearns, Jaime A, Annesley, Christopher J
• Format: Article
• Language: English
• ISSN: 1089-5639; 1520-5215
• DOI: 10.1021/acs.jpca.8b03047

Photoexcitation of water by Lyman-α (121.6 nm) induces a dissociation reaction that produces OH­(A2Σ+) + H. Despite this reaction being part of numerous studies, a combined understanding of the product and fluorescence yields is still lacking. Here, the rotational and vibrational distributions of OH­(A) are determined from dispersed fluorescence following photoexcitation of both room-temperature and jet-cooled water vapor, for the first time in the same experiment. This work compares new data of state-resolved fluorescence with literature molecular branching ratios and brings previous studies into agreement through careful consideration of OH­(A) fluorescent and predissociation lifetimes and confirms a fluorescent quantum yield of 8%. Comparison of the room-temperature and jet-cooled OH­(A) populations indicate the temperature of H2O prior to excitation has subtle effects on the OH­(A) population distribution, such as altering the rotational distribution in the ν′ = 0 population and affecting the population in the ν′ = 1 state. These results indicate jet-cooled water vapor may have a 1% higher fluorescence quantum yield compared to room-temperature water vapor.