Product branching and low temperature reaction kinetics by chirped-pulse Fourier transform mm-wave spectroscopy in a pulsed uniform supersonic flow

Dias, Nureshan

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https://hdl.handle.net/2142/104488 Copy

Description

Title

Product branching and low temperature reaction kinetics by chirped-pulse Fourier transform mm-wave spectroscopy in a pulsed uniform supersonic flow

Author(s)

Dias, Nureshan

Contributor(s)

• Broderick, Bernadette M.
• Suits, Arthur
• Suas-David, Nicolas
• Krueger, Ritter

Issue Date

2019-06-18

Keyword(s)

Dynamics and kinetics

Abstract

The CRESU technique (French acronym for “reaction kinetics in uniform supersonic flows”) has been applied with great success in the past two decades to study the kinetics of reactions at low temperatures. In this approach, a uniform low temperature flow is produced via a Laval nozzle expansion giving a wall-less reactor at constant pressure and low temperature. Product detection in that work has been either with laser-induced fluorescence directly in the flow or vacuum ultraviolet photoionization after sampling. We have recently combined low temperature Laval flows with broadband mm-wave detection (chirped-pulse/uniform flow or “CPUF”) to study product branching in photodissociation and reaction.\footnote{Oldham, J. M.; Abeysekera, C.; Joalland, B.; Zack, L. N.; Prozument, K.; Sims, I. R.; Park, G. B.; Field, R. W.; Suits, A. G. 2014, 141, 154202} Because chirped-pulse microwave detection requires monitoring the free induction decay on the timescale of microseconds, it cannot be employed at the high densities we achieve in the flows. We have used two approaches to overcome this limitation. In one, we used a “quasi-uniform” flow in which an unoptimized Laval flow was followed by a second expansion to lower temperature and density.\footnote{Dias, N.; Joalland, B.; Ariyasingha, N. M.; Suits, A. G.; Broderick, B. M. The Journal of Physical Chemistry A 2018, 122, 7523-7531.}\footnote{Broderick, B. M.; Suas-David, N.; Dias, N.; Suits, A. G. Physical Chemistry Chemical Physics 2018, 20, 5517-5529.} Detailed fluid dynamics simulations allow us to understand the temperature and density throughout that flow. Product branching can be measured under these conditions but not kinetics, as the conditions vary throughout the flow. Recently we have implemented airfoil sampling\footnote{Soorkia, S.; Liu, C.-L.; Savee, J. D.; Ferrell, S. J.; Leone, S. R.; Wilson, K. R. Review of Scientific Instruments 2011, 82, 124102.} of an optimized flow. This allows us to study low temperature kinetics as in CRESU, but with the power of broadband mm-wave spectroscopy. Recent results for several systems relevant to chemistry in cold molecular clouds and planetary atmospheres will be presented using both the quasi-uniform flow and airfoil sampling.

Publisher

International Symposium on Molecular Spectroscopy

Type of Resource

text

Language

eng

Permalink

http://hdl.handle.net/2142/104488

DOI

https://doi.org/10.15278/isms.2019.TF06

Copyright and License Information

Copyright 2019 Nureshan Dias

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