Thermochemistry of Halomethanes CFnBr4鈥?i>n (n = 0鈥?) Based on iPEPICO Experiments and Quantum Chemical Computations

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• 作者：Andras Bodi ; 脕g煤st Kvaran ; B谩lint Szt谩ray
• 刊名：Journal of Physical Chemistry A
• 出版年：2011
• 出版时间：November 24, 2011
• 年：2011
• 卷：115
• 期：46
• 页码：13443-13451
• 全文大小：1031K
• 年卷期：v.115,no.46(November 24, 2011)
• ISSN：1520-5215

文摘

Internal energy selected bromofluoromethane cations were prepared and their internal energy dependent fragmentation pathways were recorded by imaging photoelectron photoion coincidence spectroscopy (iPEPICO). The first dissociation reaction is bromine atom loss, which is followed by fluorine atom loss in CF₃Br and CF₂Br₂ at higher energies. Accurate 0 K appearance energies have been obtained for these processes, which are complemented by ab initio isodesmic reaction energy calculations. A thermochemical network is set up to obtain updated heats of formation of the samples and their dissociative photoionization products. Several computational methods have been benchmarked against the well-known interhalogen heats of formation. As a corollary, we stumbled upon an assignment issue for the ClF heat of formation leading to a 5.7 kJ mol^鈥? error, resolved some time ago, but still lacking closure because of outdated compilations. Our CF₃⁺ appearance energy from CF₃Br confirms the measurements of Asher and Ruscic ( J. Chem. Phys. 1997, 106, 210) and Garcia et al. ( J. Phys. Chem. A 2001, 105, 8296) as opposed to the most recent result of Clay et al. ( J. Phys. Chem. A 2005, 109, 1541). The ionization energy of CF₃ is determined to be 9.02鈥?.08 eV on the basis of a previous CF₃鈥揃r neutral bond energy and the CF₃ heat of formation, respectively. We also show that the breakdown diagram of CFBr₃⁺, a weakly bound parent ion, can be used to obtain the accurate adiabatic ionization energy of the neutral of 10.625 卤 0.010 eV. The updated 298 K enthalpies of formation 螖_fH^strike">o(g) for CF₃Br, CF₂Br₂, CFBr₃, and CBr₄ are reported to be 鈭?47.0 卤 3.5, 鈭?61.0 卤 7.4, 鈭?11.6 卤 7.7, and 113.7 卤 4 kJ mol^鈥?, respectively.