Study of the Stability of BrClO₃ Isomers

Abstract

The structures, vibrational frequencies, and rotational constants have been determined using ab initio methods of isomers of BrClO3. The BrOCl(O)O structural form is found to be the most stable. This species could be formed from the three-body reactions involving BrO + OClO + M → BrOCl(O)O + M and Br + ClO3 + M → BrOCl(O)O + M. The heats of reaction for these processes are estimated to be −8.2 and −24.4 kcal mol-1, respectively.

Unimolecular Dissociation of the CH3OCO Radical: An Intermediate in the CH3O + CO Reaction

“…G2M(RCC, MP2) and multichannel RRKM calculations by Mebel et al showed that the most favorable reaction pathway for this system leads to CHO + H 2 CO. 18 As part of a minor channel, the CH 3 -OCO radical can dissociate to make CH 3 + CO 2 , but the CH 3 O + CO products were not included in the analysis. The barrier for CH 3 OCO f CH 3 + CO 2 at the B3LYP/6-311G(d,p) level of theory was found to be 27.1 kcal/mol, a result similar to that of Zhou et al 15 Figure 1 shows the energetics for the CH 3 O + CO f CH 3 + CO 2 reaction at various levels of theory as calculated by Francisco, 13 Wang et al 16 and Zhou et al 15 The calculated overall reaction enthalpies are in agreement, as well as the predicted barrier heights for CH 3 OCO f CH 3 O + CO. In contrast, the energies for the CH 3 OCO f CH 3 + CO 2 transition state differ by up to 10 kcal/mol.…”

“…Francisco studied the CH 3 O + CO reaction, considering only the CH 3 + CO 2 product channel via the CH 3 OCO intermediate. 13 His QCISD(T)/6-311++G(3df,3pd) calculations predicted an entrance channel barrier of 5.8 kcal/mol and a barrier of 38.2 kcal/mol for the CH 3 OCO f CH 3 + CO 2 channel. Kang and Musgrave also calculated the CH 3 OCO f CH 3 + CO 2 reaction barrier while testing their newly developed KMLYP hybrid density-functional method.…”

Characterization of the Methoxy Carbonyl Radical Formed via Photolysis of Methyl Chloroformate at 193.3 nm

“…In the most complete study, incorporating a model for collisional stabilization of the radical intermediates, Wang et al 13 used the G2(B3LYP/MP2/CC) method to study the CH 3 O + CO reaction and performed Rice-Ramsperger-Kassel-Markus calculations to predict the products of the multiwell reaction as a function of temperature and pressure. Good et al 5 also published barriers computed at the G2 level of theory for the unimolecular dissociation of the methoxy carbonyl radical but obtained a much lower barrier, 14.7 kcal/mol, to the CH 3 + CO 2 product channel than those predicted by the work of Francisco et al, 1 Kang and Musgrave, 12 Wang et al, 13 and Zhou et al 14 In crossed laser-molecular beam studies of the CH 3 O + CO system, McCunn et al 15 measured product branching ratios under collision-free conditions for the unimolecular dissociation of the CH 3 OCO radical. The experimental results are in dramatic disagreement with predictions using the earlier high barrier calculated for the dissociation of methoxy carbonyl to methyl + CO 2 but in good agreement with the predicted branching ratio using the low barrier height of 14.7 kcal/mol predicted by Good et al 5 for the formation of CH 3 + CO 2 .…”

“…Studies on the dynamics and the energetics of combustion reaction intermediates provide vital information to facilitate this development. The methoxy carbonyl radical is an intermediate in many combustion and atmospheric chemical reactions including the methoxy + CO reaction [1][2][3] (which is integral to the methane combustion mechanism), the combustion and atmospheric oxidation of dimethyl ether, 4,5 and the combustion of dimethyl carbonate. 6 Of particular interest in the above reactions is the development of oxygenated fuels that hinder soot production by forming CO and CO 2 as combustion products.…”

“…Early theoretical work 1,[12][13][14] suggested that the dissociation of the radical to form CH 3 O + CO proceeded by a lower barrier (∼21 kcal/mol) than the barrier (∼32 kcal/mol) to the more exothermic CH 3 + CO 2 product channel, leading to the prediction that the product branching in the unimolecular dissociation of this radical under collision-free conditions would be dominated by CH 3 O + CO. In the most complete study, incorporating a model for collisional stabilization of the radical intermediates, Wang et al 13 used the G2(B3LYP/MP2/CC) method to study the CH 3 O + CO reaction and performed Rice-Ramsperger-Kassel-Markus calculations to predict the products of the multiwell reaction as a function of temperature and pressure.…”