Pressure and temperature dependence of the rate constants for the association reactions of vinoxy and 1-methylvinoxy radicals with nitric oxideElectronic supplementary information (ESI) available: Experimental conditions and results for reactions (R1) and (R2). G2 molecular properties of the key structures for CH2CHO + NO and CH2C(CH3)O + NO reaction kinetics. See http://www.rsc.org/suppdata/cp/b1/b110100e/

Abstract

The reactions of vinoxy, CH 2 CHO and 1-methylvinoxy (acetonyl) CH 2 C(CH 3 )O radicals with NO and He as a bath gas have been investigated by experimental and theoretical methods as a function of temperature and pressure (0.8-920 mbar). Two classical techniques have been used for the experiments: the discharge flow (DF) and the laser flash photolysis (LFP) techniques, both associated with a monitoring of the radicals by laser induced fluorescence. Calculations of the potential energy surface were performed using ab initio molecular orbital theory at the G2 level. Derived molecular properties of the characteristic points of the potential energy surface were used to describe the mechanism and kinetics of the reactions under investigation. The nitrosoadducts, ON-CH 2 CHO and ON-CH 2 C(CH 3 )O are predicted as the major addition products. Fall-off behavior of the reaction system was analyzed within the Troe formalism. The constructed fall-off curves allow a description of the reaction kinetics in wide ranges of pressure and temperature.The following high and low pressure limiting rate constants have been obtained:k R2;0 =½He ¼ 1:6 AE 0:5 ð ÞÂ10 À27 Â T=300 ð Þ À6:3 cm 6 molecule À2 s À1F cent;He T ð Þ ¼ 0:477 Â T=300 ð Þ À1:8

Kinetics and mechanism of the reaction of acetonyl radical, CH3C(O)CH2, with Br2

“…The current experimental and theoretical study confirms our previous conclusion [2][3][4] that acetonyl reacts like a carbon-centered free radical and not like an alkoxyl radical in its elementary reactions. Specifically, BrCH 2 C(=O)CH 3 is formed in the reaction with Br 2 , while alkoxyl radicals apparently do not enter reaction with molecular bromine [19].…”

“…The reduced reactivity can be attributed to the delocalized electronic structure of the acetonyl radical that has been observed also for the CH 3 C(O)CH 2 + O 2 [2,3] and CH 3 C(O)CH 2 + NO reactions [2][3][4]. A measure of the electron delocalization is the resonance stabilization energy (RSE), which is 23 kJ mol -1 for the acetonyl radical [10]; the "prototypical" resonance-stabilized CH 2 =CHCH 2 (allyl) and HC≡CCH 2 (propargyl) radicals have 60 and 39 kJ mol -1 RSE, respectively [10], [20].…”

“…The radical site in acetonyl is partially delocalized over the carbonyl double bond, which has been found to give rise to unusual kinetic behavior in some of the elementary reactions of this free radical [2,3]. As a continuation of our previous experimental and theoretical work [2][3][4] on the structurereactivity relations of acetonyl, we have studied the reaction of CH 3 C(O)CH 2 radical with Br 2 molecule (1). This reaction has relevance also for the enthalpy of formation of the acetonyl radical: in the classical photobromination study of acetone by King et al [5], reaction (1) was assumed to have small positive activation energy at deriving ∆ f H°2 98 (CH 3 C(O)CH 2 ), but no method was available at the time of the investigations to confirm the assumption of the authors.…”

Rate constant for the reaction of CH3C(O)CH2 radical with HBr and its thermochemical implication

“…Bouchoux et al also re‐evaluated the results of a previous experimental determination by Holmes et al 11 proposing the revised value of Δ f H (CH 3 C(O)CH 2 ) = −31.7 ± 6.4 kJ mol −1 . Recent high‐level quantum chemical computations support the new “low” values supplying −28 kJ mol −1 2, −32 ± 4 kJ mol −1 4, and −36.2 kJ mol −1 5 CH 3 C(O)CH 2 heat of formation. In view of the large disparity in the reported Δ f H (CH 3 C(O)CH 2 ) values, we have decided to re‐examine the bromination kinetics of acetone by using current experimental techniques.…”

“…Recent interest in the kinetic behavior 1–3 and thermochemical properties 4,5 of the acetonyl radical, CH 3 C(O)CH 2 , stems in a great part from the recognition of the important role this radical plays in the chemistry of the atmosphere 6,7. Acetonyl is formed in OH hydrogen abstraction reaction from acetone 7, CH 3 C(O)CH 3 , which has recently been found one of the most abundant partially oxidized organics in the atmosphere 8.…”