Thermochemistry of halogen-containing organic compounds with influence on atmospheric chemistry

Good study - need to find methods for iodinated-molecules

Details


Summary:

This research article reports a study on the thermocehemical behaviour of halogen-containing molecules in atmospheric chemical processes. The thermodynamic and thermochemical model of these components helps in understanding the interactions in both stratosphere and troposphere, particularly in ozone destruction. Precise computational analysis is reported using ab initio model and BDE (bond dissociation energies). The precision of the models was assessed using two different theoretical model chemistry Gaussian-n methods, viz. G3 and G4 for Cl and Br containing species. The G4 is reported to deliver a better performance than G3. As neither of these two are available for Iodine, MP2 level of theory with QZVP basis set was used for optimization and frequency calculations followed by single point energy calculations using QCISD(T)/QZVP.

The Reactions of Interest:

Enthalpies of formation Δfm(g) of the species in these reactions are reported in Table 1 and discussed in section 3.1.

Practical observations:

  • The performance of G3 was very well reproducible, as was that of G4. As the authors reported, I also found the G4 to be more precise for Cl and Br containing compounds on comparison with Table 1. The demarcation was however not so clear for Table 2 and Table 3.
  • QCISD(T) level of theory performed better than MP2 for Iodine containing compounds as well as radicals.

Comments:

  • The data presented in this work is very valuable for EPA.
  • As the authors have pointed out, I would also suggest further research into methods that encompass iodinated-molecules as well. That will improve the overall homogeneity of the study.


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