Temperature‐dependent kinetics study of the gas‐phase reactions of atomic chlorine with acetone, 2‐butanone, and 3‐pentanone

Abstract

A laser flash photolysis-resonance fluorescence technique has been employed to study the kinetics of the reactions of atomic chlorine with acetone (CH 3 C(O)CH 3 ; k 1 ), 2-butanone (C 2 H 5 C(O)CH 3 ; k 2 ), and 3-pentanone (C 2 H 5 C(O)C 2 H 5 ; k 3 ) as a function of temperature (210-440 K) and pressure (30-300 Torr N 2 ). No significant pressure dependence is observed for any of the reactions studied. Arrhenius expressions (units are 10 −11 cm 3 molecule −1 s −1 ) obtained from the data are k 1 (T) = (1.53 ± 0.19) exp[(−594 ± 33)/T], k 2 (T) = (2.77 ± 0.33) exp[(+76 ± 33)/T], and k 3 (T) = (5.66 ± 0.41) exp[(+87 ± 22)/T], where uncertainties are 2σ and represent precision only. The accuracy of reported rate coefficients is estimated to be ±15% over the entire range of pressure and temperature investigated. The room temperature rate coefficients reported in this study are in good agreement with a majority of literature values. However, the activation energies reported in this study are in poor agreement with the literature values, particularly for 2-butanone and 3-pentanone. Possible explanations for discrepancies in published kinetic parameters are proposed, and the potential role of Cl + ketone reactions in atmospheric chemistry is discussed. C

Temperature‐dependent rate coefficients and mechanism for the gas‐phase reaction of chlorine atoms with acetone

“…Yield measurements for re-action pathway 1b revealed that the upper limit for the adduct-formation pathway (reaction (1b)) is less than 0.1%, in the temperature range 273-363 K and at the very-low-pressure regime (<3 mTorr). The E a /R value (608 ± 16) K, obtained by absolute rate measurements, is in excellent agreement with the value (594 ± 33) K reported by Zhao et al [17]. Moreover, there is satisfactory agreement with the value (628 ± 25) K obtained by Orlando et al [15], by accepting the latest NASA/JPL Arrhenius expression for the reference reaction of Cl atoms with CH 2 Cl 2 .…”

“…4. Our study resolves the systematic discrepancy between the absolute rate measurements [9,13,17] and the consistently lower (ca. 1.3 times) relative rate determinations [11,12,14,15,26].…”

“…The results from this study can be compared with the respective ones reported by other groups, which are presented in Table III. Our room temperature k 1 values derived using both experimental techniques are in excellent agreement, and they are [17]. All rate coefficient values and Arrhenius parameters known in the literature are given in Table III, and they are presented in an Arrhenius plot for direct comparison purposes in Fig.…”

“…Although OH kinetics has been extensively studied and is well established, there are systematic discrepancies between relative rate methods [9][10][11][12][13][14][15][16] and absolute techniques, as far as the Cl kinetics is concerned [16,17]. The updated recommended room temperature value in the IUPAC review panel is based on the work from Orlando et al [15] (relative rate measurement), which, although it is consistent with most of the relative rate results, is significantly lower compared to rate coefficients obtained using absolute rate techniques.…”

“…The updated recommended room temperature value in the IUPAC review panel is based on the work from Orlando et al [15] (relative rate measurement), which, although it is consistent with most of the relative rate results, is significantly lower compared to rate coefficients obtained using absolute rate techniques. Recently and while this work was in progress, Zhao et al [17] measured the temperature dependence of the rate coefficient for the gas-phase reaction of Cl atoms with CH 3 C(O)CH 3 , employing the laser flash photolysisresonance fluorescence (LFP-RF) technique. To the best of our knowledge, Zhao et al (absolute rate coefficient determination) and Orlando et al (relative rate methods) are the only studies existing in the literature that report temperature-dependent rate coefficients for the title reaction.…”