Ab initio calculations at the G2 level were used in a theoretical analysis of the kinetics of unimolecular and water-accelerated decomposition of the halogenated alcohols CX(3)OH (X = F, Cl, and Br) into CX(2)O and HX. The calculations show that reactions of the unimolecular decomposition of CX(3)OH are of no importance under atmospheric conditions. A considerably lower energy pathway for the decomposition of CX(3)OH is accessible by homogenous reactions between CX(3)OH and water. It is shown that CX(3)OH + H(2)O reactions proceed via the formation of intermediate complexes. The mechanism of the reactions appears to be complex and consists of three consecutive elementary processes. The calculated values of the second-order rate constants are of 2.5 x 10(-21), 2.1 x 10(-19), and 1.2 x 10(-17) cm(3)molecule(-1)s(-1) at 300 K for CF(3)OH + H(2)O, CCl(3)OH + H(2)O, and CBr(3)OH + H(2)O, respectively. The theoretically derived atmospheric lifetimes of the CX(3)OH molecules indicate that the water-mediated decomposition reactions CX(3)OH + H(2)O may be the most efficient process of CF(3)OH, CCl(3)OH, and CBr(3)OH loss in the atmosphere.
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
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