Arrhenius Behavior of Electron Attachment to CH3Br from 303 to 1100 K
Abstract
Thermal electron attachment to CH3Br has been studied over the temperature range 303-1100 K using two flowing-afterglow Langmuir-probe apparatuses. The reaction yielded only Br- product over this temperature range. The rate coefficient for electron attachment to CH3Br was measured to be 8 +/- 4 10^-12 cm^3 s^-1 at 303 K, and was observed to increase strongly with gas temperature. Rate coefficients for the reaction show Arrhenius behavior over the entire temperature range with an activation energy of 260 +/- 20 meV. The results are in substantial agreement with earlier data covering a smaller temperature range. Kinetic modeling implies that this behavior and the small rate coefficient at room temperature are due to a barrier in the crossing from the neutral to the anionic potential surfaces of approximately 280 meV that dominates other factors in the attachment reaction. There is a hint of the Arrhenius plot reaching saturation at the highest temperatures. While examining an electron-cation recombination correction, the rate coefficient (1.8 +/- 0.4 10^-9 cm^3 s^-1) of the reaction Ar+ + CH3Br was measured at 302 K, and the ion products identified (80% CH3+ and 20% CH2Br+). A secondary reaction forming the adduct (CH3Br)CH3+ was seen to occur with a rate coefficient of 2.8 +/- 1.0 10^-9 cm^3 s^ 1.
Document Details
- Document Type
- Technical Report
- Publication Date
- Dec 21, 2013
- Accession Number
- ADA626685
Entities
People
- Albert A Viggiano
- Nicholas S Shuman
- Thomas M Miller
Organizations
- Air Force Research Laboratory