Kinetics of the Reactions of O(³P) with CCl₂CH₂, (Z)-CHClCHCl, and CCl₂CCl₂: A Temperature Dependence Study

Abstract

Absolute rate coefficients for the gas-phase reactions of ground-state oxygen atoms with CCl(2)=CH(2) (1), (Z)-CHCl=CHCl (2) and CCl(2)=CCl(2) (3) have been measured directly using the fast flow discharge technique. The experiments were carried out under pseudo-first-order conditions with [O((3)P)](0) << [chloroethene](0). The temperature dependences of the reactions of O((3)P) with CCl(2)=CH(2), (Z)-CHCl=CHCl and CCl(2)=CCl(2) were studied in the range 298-359 K. The kinetic data obtained were used to derive the following Arrhenius expressions (in units of cm(3) molecule(-1) s(-1)): k(1) = (1.82 +/- 1.29) x 10(-11) exp[-(12.63 +/- 0.97) x 10(3)/RT], k(2) = (1.56 +/- 0.92) x 10(-11) exp[-(16.68 +/- 1.54) x 10(3)/RT], k(3) = (4.63 +/- 1.38) x 10(-11) exp[-(19.59 +/- 3.21) x 10(3)/RT]. This is the first temperature dependence study of the reactions of O((3)P) atoms with (Z)-CHCl=CHCl and CCl(2)=CCl(2). All the rate coefficients display a positive temperature dependence and pressure independence, which points to the importance of the irreversibility of the addition mechanism for these reactions. The obtained rate coefficients are compared with previous studies carried out mainly at room temperature. The rates of addition of O atoms and OH radicals to the double bond of alkenes at 298 K are related by the expression: log k(OH) = 0.57278 log k(O(3P)) - 4.095. A correlation is presented between the reactivity of chloroethenes toward O atoms and the second-order perturbational term of the frontier molecular orbital theory which carries the contribution of the different atomic orbitals to the HOMO of the chloroethene. To a first approximation, this correlation allows room-temperature rate coefficients to be predicted within +/-25-30% of the measured values.

Gas phase kinetics for the ozonolysis of n-butyl methacrylate, ethyl crotonate and vinyl propionate under atmospheric conditions

“…The results are discussed in terms of the effect of the position of the methyl substituent, the ester functionality, and the double bond on the reactivity of the compounds towards O 3 molecules. This study complements ongoing work in our laboratories to understand the factors that contribute to the reactivity of unsaturated VOCs with different tropospheric oxidants O( 3 P) [10], OH [3][4][5]11] and Cl [5][6][7]11,12].…”

“…An electrical discharge in a flow of pure oxygen was used to generate ozone. The initial concentrations of reactants in ppmV (1 ppmV = 2.46 Â 10 13 molecule cm À3 at 298 K) were: n-butyl methacrylate, (8)(9); vinyl propionate, (7-9); ethyl crotonate, (10)(11)(12); ozone, (1-2); carbon monoxide, (34-41); isobutene, (15)(16)(17)(18); 1,3-butadiene, (16)(17)(18)(19) and cyclohexene, (14)(15)(16)(17)(18). The reactants were monitored at the following infrared absorption frequencies (in cm À1 ): n-butyl methacrylate at 1169; vinyl propionate at 1174; ethyl crotonate at 1186; isobutene at 890; 1,3-butadiene at 908 and cyclohexene at 3000 and 2840.…”

OH-Initiated Degradation of Unsaturated Esters in the Atmosphere: Kinetics in the Temperature Range of 287−313 K

“…The results are discussed in terms of the effect that the position of the methyl substituent, ester functionality, and double bond have on the reactivity of the compounds toward OH radicals. This study complements ongoing work in our laboratories to understand the factors that contribute to the reactivity of unsaturated VOCs toward different tropospheric oxidants (O( 3 P), OH, − , and Cl).…”

Study of the Vibrational Spectra and Absorption Cross Sections of 1-Chloro-1-fluoroethene by a Joint Experimental and Ab Initio Approach

“…They can be employed as test molecules to compare different approaches and therefore, many theoretical works focusing on the prediction of properties including, for example, stabilities, , thermochemical data, on their use for benchmarking accurate equilibrium structures, , and on the performances of different computational methods , have been recently published for some of them. Being considered trace gas pollutants, the kinetics of their reactions with O­( 3 P), and their photochemistry , and adsorption − on substrates suitable for subsequent photodegradation have also been investigated. For supporting the monitoring by means of spectroscopic techniques studies dealing with the computation of the vibrational frequencies, the analysis of resonances and determination of anharmonic constants from the assignments of low-resolution infrared spectra have been carried out for some halogenated ethenes. − …”

“…Reliable band assignments combined with accurate modeling of vibrational couplings and high-level ab initio calculations provide the detailed basic data that, − coupled to the different experimental methods developed for reducing the spectral congestion (for example the use of cooling cells, − and supersonic jet expansion − ) and with the aid by sophisticated data-processing techniques, − are necessary to guide and support the rovibrational analysis. In addition to the spectroscopic interest due to the environmental issues related to the presence of haloethenes in the atmosphere, the potential threat to the stratospheric ozone layer related to their photodissociation and corresponding release of halogen atoms motivated many studies on the elimination mechanisms and distributions of kinetic energy, − the kinetics of their reactions with O­( 3 P), and their photochemistry. , …”