Search

The reactions of Cl with a series of linear thiols: 1-propanethiol (k(1)), 1-butanethiol (k(2)), and 1-pentanethiol (k(3)) were investigated as a function of temperature (in the range of 268-379 K) and pressure (in the range of 50-200 Torr) by laser photolysis-resonance fluorescence. Only 1-propanethiol has previously been studied, but at 1 Torr of total pressure. The derived Arrhenius expressions obtained using our kinetic data were as follows: k(1)=(3.97+/-0.44)x10(-11) exp[(410+/-36)T], k(2)=(1.01+/-0.16)x10(-10) exp[(146+/-23)T], and k(3)=(1.28+/-0.10)x10(-10) exp[(129+/-25)T] (in units of cm(3) molecule(-1) s(-1)). Moreover, a theoretical insight into mechanisms of these reactions has also been pursued through ab initio Moller-Plesset second-order perturbation treatment calculations with 6-311G(**) basis set. Optimized geometries have been obtained for transition states and molecular complexes appearing along the different reaction pathways. Furthermore, molecular energies have been calculated at QCISD(T) level in order to get an estimation of the activation energies. Finally, the nature of the molecular complexes and transitions states is analyzed by using kinetic-potential and natural bond orbital total energy decomposition schemes.

An absolute kinetic study of the reaction of Cl atoms with CF3CF2CH2OH is reported as a function of temperature (T = 268–377 K) and at a total pressure of 100 Torr by the Pulsed Laser Photolysis - Resonance Fluorescence (PLP-RF) technique. No pressure dependence of the rate coefficient for the title reaction,k, was observed between 50 and 200 Torr of He at 298 K. The derived Arrhenius expression in thatT-range wask(T) = (2.18 ± 0.24) × 10−12exp(–(333 ± 34)/T) cm3molecule−1 s−1, where the uncertainties are ±2σ. From these results, the average tropospheric lifetime of CF3CF2CH2OH due to the reaction with Cl was estimated to be 50 years, considering a global Cl concentration of 103atom cm−3and an average temperature of 272 K. Additionally, a theoretical study of the Cl + CF3CF2CH2OH reaction has been carried out byab initioMöller–Plesset second-order perturbation treatment with 6-311G** basis set to investigate the reaction mechanism. Molecular energies of the different critical points of the potential energy surface have been calculated at QCISD(T) level. The theoretical study shows that the H-atom abstraction from the –CH2– group is the most favourable reaction pathway. [ABSTRACT FROM AUTHOR]

Abstract: Laser photolysis-resonance fluorescence was used for the first time to investigate the reaction of ethanethiol with atmospheric relevant Cl atoms as a function of temperature and pressure. Kinetic data obtained were used to derive an Arrhenius expression. Moreover, a mechanism is proposed on the base of ab initio MP2/6-311G** calculations. Activation energies have been estimated through QCISD(T) molecular energies. Accordingly, our results predict, for the first time, two nearly energy-equivalent channels for H-abstraction from CH3CH2SH under attack by Cl, one showing attack along H–S bond whereas the other exhibits attack along H–C α bond. [Copyright &y& Elsevier]

The reaction of Cl with cyclohexanone (1) was investigated, for the first time, as a function of temperature (273–333 K) and at a low total pressure (1 Torr) with helium as a carrier gas using a discharge flow-mass spectrometry technique (DF-MS). The resulting Arrhenius expression is proposed, k1 = (7.7 ± 4.1) × 10-10 exp[–(540 ± 169)/T]. We also report a mechanistic study with the quantitative determination of the products of the reaction of Cl with cyclohexanone. The absolute rate constant derived from this study at 1 Torr of total pressure and room temperature is (1.3 ± 0.2) × 10-10 cm3 molecule-1 s-1. A yield of 0.94 ± 0.10 was found for the H-abstraction channel giving HCl. In relative studies, using a newly constructed relative rate system, the decay of cyclohexanone was followed by gas chromatography coupled with flame-ionisation detection. These relative measurements were performed at atmospheric pressure with synthetic air and room temperature. Rate constant measured using the relative method for reaction (1) is: (1.7 ± 0.3) × 10-10 cm3 molecule-1 s-1. Finally, results and atmospheric implications are discussed and compared with the reactivity with OH radicals. [ABSTRACT FROM AUTHOR]

The article presents the author's insights regarding the improper operation of the experimental system at low temperatures in the study that examines the kinetics of the reaction of chlorine (Cl) atoms with three 2-buten-1-ol, 2-methyl-2-propen-1-ol, and 3-methyl-2-buten-1-ol.

Abstract: In this work, the reactions of Cl with a series of secondary alcohols: 2-butanol, 2-methyl-2-butanol, 3-methyl-2-butanol, and 2,3-dimethyl-2-butanol have been studied through ab initio Möller–Plesset second order perturbation treatment (MP2) calculations with 6-311G∗∗ basis sets. Optimized geometries and vibrational frequencies have been obtained for transition states and molecular complexes appearing along the different reaction pathways. Furthermore, molecular energies have been calculated at Quadratic Configuration Interaction with Single, Double, and Triple Excitations (QCISD(T)) level in order to get an estimation of activation barriers. The theoretical rate constant was also calculated for the main reaction pathways using the Transition State Theory. The main aim of this work is to extend, from a theoretical point of view, the knowledge of this kind of reactions that play a significant role in atmospheric chemistry. [Copyright &y& Elsevier]

Abstract: The products of the chlorine atom initiated oxidation of different unsaturated alcohols were determined at atmospheric pressure and ambient temperature, in a 400 L teflon reaction chamber using GC–FID and GC–MS for the analysis. The major products detected (with molar yields in brackets) are: chloroacetaldehyde (50 ± 8%) and acrolein (27 ± 2%) from allyl alcohol; acetaldehyde (77 ± 11%), chloroacetaldehyde (75 ± 18%), and methyl vinyl ketone (17 ± 2%) from 3-buten-2-ol; acetone (55 ± 4%) and chloroacetaldehyde (59 ± 8%) from 2-methyl-3-buten-2-ol; chloroacetone (18 ± 1%) and methacrolein (8 ± 1%) from 2-methyl-2-propen-1-ol; acetaldehyde (20 ± 1%), crotonaldehyde (6 ± 3%), 3-choloro-4-hydroxy-2-butanone (2 ± 2%) and 2-chloro-propanal (4 ± 5%) from crotyl alcohol; and acetone (24 ± 3%) from 3-methyl-2-buten-1-ol. The experimental data suggests that addition of Cl to the double bond of the unsaturated alcohol is the dominant reaction pathway compared to the H-abstraction channel. [Copyright &y& Elsevier]