Application of external-cavity quantum cascade infrared lasers to nanosecond time-resolved infrared spectroscopy of condensed-phase samples following pulse radiolysis.

Chemistry Department, Brookhaven National Laboratory, Upton, New York 11973-5000, USA.
Applied Spectroscopy (Impact Factor: 1.94). 06/2010; 64(6):563-70. DOI: 10.1366/000370210791414344
Source: PubMed

ABSTRACT Pulse radiolysis, utilizing short pulses of high-energy electrons from accelerators, is a powerful method for rapidly generating reduced or oxidized species and other free radicals in solution. Combined with fast time-resolved spectroscopic detection (typically in the ultraviolet/visible/near-infrared), it is invaluable for monitoring the reactivity of species subjected to radiolysis on timescales ranging from picoseconds to seconds. However, it is often difficult to identify the transient intermediates definitively due to a lack of structural information in the spectral bands. Time-resolved vibrational spectroscopy offers the structural specificity necessary for mechanistic investigations but has received only limited application in pulse radiolysis experiments. For example, time-resolved infrared (TRIR) spectroscopy has only been applied to a handful of gas-phase studies, limited mainly by several technical challenges. We have exploited recent developments in commercial external-cavity quantum cascade laser (EC-QCL) technology to construct a nanosecond TRIR apparatus that has allowed, for the first time, TRIR spectra to be recorded following pulse radiolysis of condensed-phase samples. Near single-shot sensitivity of DeltaOD <1 x 10(-3) has been achieved, with a response time of <20 ns. Using two continuous-wave EC-QCLs, the current apparatus covers a probe region from 1890-2084 cm(-1), and TRIR spectra are acquired on a point-by-point basis by recording transient absorption decay traces at specific IR wavelengths and combining these to generate spectral time slices. The utility of the apparatus has been demonstrated by monitoring the formation and decay of the one-electron reduced form of the CO(2) reduction catalyst, [Re(I)(bpy)(CO)(3)(CH(3)CN)](+), in acetonitrile with nanosecond time resolution following pulse radiolysis. Characteristic red-shifting of the nu(CO) IR bands confirmed that one-electron reduction of the complex took place. The availability of TRIR detection with high sensitivity opens up a wide range of mechanistic pulse radiolysis investigations that were previously difficult or impossible to perform with transient UV/visible detection.

  • [Show abstract] [Hide abstract]
    ABSTRACT: The field of ultrafast spectroscopy includes the spectroscopic measurements for which electronic detectors are not fast enough to allow direct measurement of phenomena. These time scales presently range from about 10 fs to 100 ps, a period that encompasses a wealth of interesting chemical processes. In this field, the techniques and their chemical applications are inextricably tied together, and any thorough treatment must include both. In his monograph, Graham Fleming accomplishes the challenging task of fully describing both the technological and the chemical ends of ultrafast spectroscopy. Fleming is a recognized leader in the area of ultrafast spectroscopy who has made important contributions to techniques and chemical studies. Three chapters of the book are devoted to technology: methods of generating short pulses, methods of characterizing them, and techniques for using them in chemical experiments. The large number of chemical applications are covered in the remaining three chapters: relaxation processes in vapors, in liquid phases, and in solid phases.
  • Source
    Electron Transfer in Chemistry, 04/2008: pages 558 - 592; , ISBN: 9783527618248

Full-text (2 Sources)

Available from
May 29, 2014