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

David Grills, Andrew R. Cook, Etsuko Fujita, Michael W. George, Jack M. Preses, James F. Wishart

Research output: Contribution to journalArticle

22 Citations (Scopus)

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 gasphase 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 AOD -3 has been achieved, with a response time of -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 CO2 reduction catalyst, [Re1(bPy)(CO) 3(CH3CN)]+, in acetonitrile with nanosecond time resolution following pulse radiolysis. Characteristic red-shifting of the v(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. & 2010 Society for Applied Spectroscopy.

Original languageEnglish
Pages (from-to)563-570
Number of pages8
JournalApplied Spectroscopy
Volume64
Issue number6
Publication statusPublished - Jun 2010

Fingerprint

Radiolysis
Infrared lasers
quantum cascade lasers
radiolysis
infrared lasers
Infrared spectroscopy
infrared spectroscopy
cavities
Infrared radiation
pulses
Carbon Monoxide
Electrons
Vibrational spectroscopy
Quantum cascade lasers
Monitoring
Acetonitrile
Free radicals
infrared spectra
Free Radicals
Particle accelerators

Keywords

  • EC-QCL
  • External-cavity quantum cascade laser
  • Nanosecond time-resolved infrared spectroscopy
  • Pulse radiolysis
  • TRIR

ASJC Scopus subject areas

  • Spectroscopy
  • Instrumentation

Cite this

Application of external-cavity quantum cascade infrared lasers to nanosecond time-resolved infrared spectroscopy of condensed-phase samples following pulse radiolysis. / Grills, David; Cook, Andrew R.; Fujita, Etsuko; George, Michael W.; Preses, Jack M.; Wishart, James F.

In: Applied Spectroscopy, Vol. 64, No. 6, 06.2010, p. 563-570.

Research output: Contribution to journalArticle

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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 gasphase 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 AOD -3 has been achieved, with a response time of -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 CO2 reduction catalyst, [Re1(bPy)(CO) 3(CH3CN)]+, in acetonitrile with nanosecond time resolution following pulse radiolysis. Characteristic red-shifting of the v(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. & 2010 Society for Applied Spectroscopy.",
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