Development of nanosecond time-resolved infrared detection at the LEAF pulse radiolysis facility

• Published in: Review of scientific instruments 2015-04, Vol.86 (4)
• Main Authors: Grills, David C., Farrington, Jaime A., Layne, Bobby H., Preses, Jack M., Wishart, James F., Bernstein, Herbert J.
• Format: Article
• Language: English
• Subjects: ABSORPTION; ABSORPTION SPECTROSCOPY; BEAMS; DETECTION; ELECTRON TRANSFER; INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND TECHNOLOGY; KINETICS; LASERS; PROBES; PULSES; RADIOLYSIS; REACTION INTERMEDIATES; SENSITIVITY; TIME RESOLUTION
• ISSN: 0034-6748; 1089-7623

When coupled with transient absorption spectroscopy, pulse radiolysis, which utilizes high-energy electron pulses from an accelerator, is a powerful tool for investigating the kinetics and thermodynamics of a wide range of radiation-induced redox and electron transfer processes. The majority of these investigations detect transient species in the UV, visible, or near-IR spectral regions. Unfortunately, the often-broad and featureless absorption bands in these regions can make the definitive identification of intermediates difficult. Time-resolved vibrational spectroscopy would offer much improved structural characterization, but has received only limited application in pulse radiolysis. In this paper, we describe in detail the development of a unique nanosecond time-resolved infrared (TRIR) detection capability for condensed-phase pulse radiolysis on a new beam line at the LEAF facility of Brookhaven National Laboratory. The system makes use of a suite of high-power, continuous wave external-cavity quantum cascade lasers as the IR probe source, with coverage from 2330 to 1051 cm{sup −1}. The response time of the TRIR detection setup is ∼40 ns, with a typical sensitivity of ∼100 μOD after 4-8 signal averages using a dual-beam probe/reference normalization detection scheme. This new detection method has enabled mechanistic investigations of a range of radiation-induced chemical processes, some of which are highlighted here.