Infrared chemiluminescence studies of the reactions of H atoms with CCl₃, CF₂Cl, and CH₂CH₂Cl radicals at 300 and 475 K: recombination–elimination vs. abstraction mechanisms

Abstract

. Can. J. Chem. 72,568 (1994). The reactions of H atoms with CC13, CF2C1, and CH2CH2C1 radicals have been studied in a flow reactor at 300 and 475 K by observation of the infrared emission from the HC1 and HF products. These reactions were observed as secondary reactions from the H + CC13Br, CF2C1Br, and CH2C1-CH21 chemical systems. The conditions in the flow reactor were controlled so that the nascent vibrational distributions of HC1 and HF were recorded. The pattern of vibrational energy disposal to HC1 was used to differentiate between C1 atom abstraction and recombination-elimination mechanisms. The H atom reactions with CC13 and CF2C1 radicals occur only via a recombination+limination mechanism and give HCl(v) or HF(v) in a unimolecular step. Thus, the C1 atom abstraction reactions must have 23.0 kcal mol-' higher activation energy than the recombination reaction. From observation of the ratio of the HC1 and HF products from CHF2C1*, the difference in threshold energies for HF and HC1 elimination was determined to be -13 kcal mol-'. On the other hand, ~1 atom abstraction does compete with recombination+limination in the H + CH2CH2C1 reaction, the branching fraction is -0.3 at 300 K and -0.6 at 475 K.

The direct production of CO(v=1–9) in the reaction of O(3P) with the ethyl radical

“…The monotonically decreasing nascent CO vibrational distribution suggests that the reaction does proceed through a complex, supporting the ideas postulated above. [37][38][39][40] However, as for the reaction of O( 3 P) with CH 3 , it is difficult to envisage any direct mechanism which could lead to the production of CO(v).…”

Roaming dynamics in radical addition–elimination reactions

“…However, the details of the reaction mechanism and dynamics remain unknown. State-selected HCl measurements have not shown a distinct feature of addition-elimination in the product distributions 13 . Quantum chemical calculations of reaction potential energy surfaces (PESs) have been unable to corroborate the additionelimination mechanism 14,15 .…”

Dynamics of Chlorine Atom Reactions with Hydrocarbons: Insights from Imaging the Radical Product in Crossed Beams

“…35,36 The formation of HCl(v′=1) products has been attributed to direct reactions, whereas addition− elimination was assumed to give low vibrational excitation due to energy randomization in the long-lived adduct. 37 We will revisit this point in what follows.…”