HIGH RESOLUTION MICROWAVE SPECTROSCOPY IN A CRYOGENIC BUFFER GAS CELL: BRANCHING RATIOS AND REACTIVE INTERMEDIATES IN THE OZONOLYSIS OF ISOPRENE

Porterfield, Jessie P.

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https://hdl.handle.net/2142/100793 Copy

Description

Title

HIGH RESOLUTION MICROWAVE SPECTROSCOPY IN A CRYOGENIC BUFFER GAS CELL: BRANCHING RATIOS AND REACTIVE INTERMEDIATES IN THE OZONOLYSIS OF ISOPRENE

Author(s)

Porterfield, Jessie P.

Contributor(s)

• McCarthy, Michael C.
• Patterson, David
• Eibenberger, Sandra

Issue Date

06/22/18

Keyword(s)

Atmospheric science

Abstract

A new method to quantify reaction product ratios using high resolution microwave spectroscopy in a cryogenic buffer gas cell has been developed. We demonstrate its power with product ratio quantification in the ozonolysis of isoprene, \ce{CH2=C(CH3)-CH=CH2}, the most abundant, non-methane hydrocarbon emitted into the atmosphere by vegetation. Purified \ce{O3} and isoprene were mixed for approximately 10\,s under dilute (1.5-4\% in argon) continuous flow conditions in an alumina tube held at 298 K and 5 Torr. Products exiting the tube were rapidly slowed and cooled within the buffer gas cell by collisions with cryogenic (4-7\,K) He. High resolution chirped pulse microwave detection between 12 and 26\,GHz was used to achieve isomer-specific product quantification with ppb sensitivity. \begin{wrapfigure}{r}{0pt} \includegraphics[scale=0.59]{graphical_abstract_ISMS.eps} \end{wrapfigure} We determined a ratio of MACR to MVK of 2.1 $\pm$ 0.4 under 1:1 ozone to isoprene conditions and 2.1 $\pm$ 0.2 under 2:1 ozone to isoprene conditions, a finding which is consistent with previous experimental results. The potential to perform a complete branching ratio analysis is discussed using $^{13}$C isotopic substitution of isoprene. We also discuss the prospects for detecting the proposed Criegee intermediates in this reaction, methacrolein-oxide and methyl vinyl ketone-oxide, neither of which have ever been observed.

Publisher

International Symposium on Molecular Spectroscopy

Type of Resource

text

Language

English

Permalink

http://hdl.handle.net/2142/100793

DOI

10.15278/isms.2018.FF08

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