A white cell based broadband transient UV-vis absorption spectroscopy with pulsed laser photolysis reactors for chemical kinetics under variable temperatures and pressures
Creators
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1.
Jet Propulsion Lab
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2.
California Institute of Technology
Abstract
UV-vis spectroscopy is widely used for kinetic studies in physical chemistry, as species' absolute cross-sections are usually less sensitive to experimental conditions (i.e., temperature and pressure). Here, we present the design and characterization of a multipass UV-vis absorption spectroscopy white cell coupled to a pulsed-laser photolysis flow reactor. The glass reactor was designed to facilitate studies of gas phase chemical reactions over a range of conditions (239–293 K and 10–550 Torr). Purged windows mitigate contamination from chemical precursors and photolysis products. We report the measured impact of this purging on temperature uniformity and the absorption length and present some supporting flow calculations. The combined optical setup is unique and enables the photolysis laser to be coaligned with a well-defined absorption pathlength probe beam. This alignment leverages the use of one long-pass filter to increase the spectrum flatness and increase the light intensity vs other systems that use two dichroic mirrors. The probe beam is analyzed with a dual exit spectrograph, customized to split the light between an intensified CCD and photomultiplier tube, enabling simultaneous spectrum and single wavelength detection. This multipass system yields a pathlength of ∼450 cm and minimum observable concentrations of ∼3.7 × 10¹¹ molecule cm⁻³ (assuming cross-sections ∼1.2 × 10−17 cm²). The temperature profile across the reaction region is ±2 K, defined by the worst-case temperature of 239 K, validated by measurements of the N₂O₄ equilibrium constant. Finally, the system is implemented to study the simplest Criegee intermediate, demonstrating the instrument performance and advantages of simultaneous spectrum and temporal profile measurements.
Copyright and License
© 2023 Author(s). Published under an exclusive license by AIP Publishing.
Acknowledgement
The experimental research herein was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration (NASA). Financial support was provided by the NASA Upper Atmosphere Research, Tropospheric Composition and Solar System Workings programs and the J. Yang and Family Foundation. Rebecca Caravan's research was supported by an appointment to the NASA Postdoctoral Program, administered by the Universities Space Research Association under contract with NASA. We would like to acknowledge Mitchio Okumura for useful discussion and guidance around the characterization of the instrument and initial results.
Contributions
Frank A. F. Winiberg: Conceptualization (lead); Investigation (equal); Methodology (lead); Resources (lead); Software (lead); Supervision (equal); Validation (equal); Writing – original draft (lead). Wen Chao: Data curation (lead); Formal analysis (lead); Investigation (lead); Methodology (equal); Validation (lead); Visualization (lead); Writing – original draft (equal); Writing – review & editing (equal). Rebecca L. Caravan: Conceptualization (equal); Methodology (supporting); Writing – original draft (equal); Writing – review & editing (equal). Charles R. Markus: Conceptualization (equal); Writing – original draft (supporting); Writing – review & editing (equal). Stanley P. Sander: Conceptualization (supporting); Funding acquisition (supporting); Project administration (equal); Supervision (supporting); Validation (supporting); Writing – review & editing (equal). Carl J. Percival: Conceptualization (supporting); Data curation (supporting); Funding acquisition (lead); Project administration (lead); Supervision (lead); Writing – original draft (supporting); Writing – review & editing (equal).
Data Availability
The data that support the findings of this study are available from the corresponding author upon reasonable request.
Conflict of Interest
The authors have no conflicts to disclose.
Files
114103_1_5.0164733.pdf
Additional details
Identifiers
- ISSN
- 1089-7623
Funding
- National Aeronautics and Space Administration
- Jet Propulsion Laboratory
- California Institute of Technology
- J. Yang and Family Foundation
- NASA Postdoctoral Program