Journal
JOURNAL OF CHEMICAL PHYSICS
Volume 138, Issue 15, Pages -Publisher
AMER INST PHYSICS
DOI: 10.1063/1.4801657
Keywords
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Funding
- (U.S.) Air Force Office of Scientific Research (USAFOSR) [AFOSR-2303EP]
- National Research Council
- Air Force Research Laboratory through the Space Scholars Program
- Department of Defense
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A novel technique using a flowing afterglow-Langmuir probe apparatus for measurement of temperature dependences of rate constants for dissociative recombination (DR) is presented. Low (similar to 10(11) cm(-3)) concentrations of a neutral precursor are added to a noble gas/electron afterglow plasma thermalized at 300-500 K. Charge exchange yields one or many cation species, each of which may undergo DR. Relative ion concentrations are monitored at a fixed reaction time while the initial plasma density is varied between 10(9) and 10(10) cm(-3). Modeling of the decrease in concentration of each cation relative to the non-recombining noble gas cation yields the rate constant for DR. The technique is applied to several species (O-2(+), CO2+, CF3+, N2O+) with previously determined 300 K values, showing excellent agreement. The measurements of those species are extended to 500 K, with good agreement to literature values where they exist. Measurements are also made for a range of CnHm+ (C7H7+, C7H8+, C5H6+, C4H4+, C6H5+, C3H3+, and C6H6+) derived from benzene and toluene neutral precursors. CnHm+ DR rate constants vary from 8-12 x 10(-7) cm(3) s(-1) at 300 K with temperature dependences of approximately T-0.7. Where prior measurements exist these results are in agreement, with the exception of C3H3+ where the present results disagree with a previously reported flat temperature dependence. (C) 2013 AIP Publishing LLC. [http://dx.doi.org/10.1063/1.4801657]
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