High resolution microwave spectroscopy in a cryogenic buffer gas cell: Branching ratios and reactive intermediates in the ozonolysis of isoprene

Porterfield, Jessie P.

Permalink

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

2018-06-22

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, CH2−−C(CH3 )−CH−−CH2 , the most abundant, non-methane hydrocarbon emitted into the atmosphere by vegetation. Purified 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. trans-isoprene CH3 H O3 2C CH2 + CH3 H2C O C CH3 O CH2 + 2 methacrolein : 1 methyl vinyl ketone carbonyl oxide O O CH2 + - MACR-oxide O + OCH3 H2C C CH3 O MVK-oxide - O + CH2 We determined a ratio of MACR to MVK of 2.1 ± 0.4 under 1:1 ozone to isoprene conditions and 2.1 ± 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 13C isotopic substitution of isoprene. We also discuss the prospects for detecting the proposed Criegee intermediates in this reaction, methacrolein-oxide and methyl vinyl ketoneoxide, neither of which have ever been observed.

Publisher

International Symposium on Molecular Spectroscopy

Type of Resource

text

Language

eng

Permalink

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

DOI

10.15278/isms.2018.FF08

Copyright and License Information

Copyright 2018 Jessie P. Porterfield

Owning Collections