@Article{C8CP02055H,
author ="Porterfield, Jessica P. and Eibenberger, Sandra and Patterson, David and McCarthy, Michael C.",
title  ="The ozonolysis of isoprene in a cryogenic buffer gas cell by high resolution microwave spectroscopy",
journal  ="Phys. Chem. Chem. Phys.",
year  ="2018",
volume  ="20",
issue  ="24",
pages  ="16828-16834",
publisher  ="The Royal Society of Chemistry",
doi  ="10.1039/C8CP02055H",
url  ="http://dx.doi.org/10.1039/C8CP02055H",
abstract  ="We have developed a method to quantify reaction product ratios using high resolution microwave spectroscopy in a cryogenic buffer gas cell. We demonstrate the power of this method with the study of the ozonolysis of isoprene{,} CH2[double bond{,} length as m-dash]C(CH3)-CH[double bond{,} length as m-dash]CH2{,} the most abundant{,} non-methane hydrocarbon emitted into the atmosphere by vegetation. Isoprene is an asymmetric diene{,} and reacts with O3 at the 1{,}2 position to produce methyl vinyl ketone (MVK){,} formaldehyde{,} and a pair of carbonyl oxides: [CH3CO-CH[double bond{,} length as m-dash]CH2 + CH2[double bond{,} length as m-dash]OO] + [CH2[double bond{,} length as m-dash]O + CH3COO-CH[double bond{,} length as m-dash]CH2]. Alternatively{,} O3 could attack at the 3{,}4 position to produce methacrolein (MACR){,} formaldehyde{,} and two carbonyl oxides [CH2[double bond{,} length as m-dash]C(CH3)-CHO + CH2[double bond{,} length as m-dash]OO] + [CH2[double bond{,} length as m-dash]O + CH2[double bond{,} length as m-dash]C(CH3)-CHOO]. Purified O3 and isoprene were mixed for approximately 10 seconds 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 highly sensitive (ppb scale){,} isomer-specific product quantification. We observed 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. Additionally{,} we discuss relative quantities of formic acid (HCOOH){,} an isomer of CH2[double bond{,} length as m-dash]OO{,} and formaldehyde (CH2[double bond{,} length as m-dash]O) under varying experimental conditions{,} and characterize the spectroscopic parameters of the singly-substituted 13C trans-isoprene and 13C anti-periplanar-methacrolein species. This work has the potential to be extended towards a complete branching ratio analysis{,} as well towards the ability to isolate{,} identify{,} and quantify new reactive intermediates in the ozonolysis of alkenes."}