Evaluating Data for Atmospheric Models, an Example: IO + NO2 = IONO2

Pressure dependent reactions for atmospheric and combustion models

In order to characterize reactions as functions of temperature, pressure (molecular density) and the nature of the species that constitute that molecular density, master equation solutions are required. In this tutorial review, the application of the Multiwell suite of codes to some reactions of interest in atmospheric and combustion chemistry is discussed, with attention given to the details of the molecular and energy transfer values. Uncertainties in data and in structural and energetic molecular parameters combine to assure the need for optimization and collaborative processing of the entire data base when modeling practical systems.

The Reaction Cl + NO2 → ClONO and ClNO2

The extant data (see Int. J. Chem. Kinet. 1984, 16, 1311; Int. J. Chem. Kinet. 1988, 20, 811; and J. Phys. Chem. 1996, 100, 4019)1-3 for the reaction of Cl atoms with NO2 has been examined and compared with calculated values using RRKM/ME methods through the use of the coded suite "Multiwell" (see Int. J. Chem. Kinet. 2001, 33, 232; MultiWell-2.08 Software; University of Michigan: Ann Arbor, MI, 2007; http://aoss.engin.umich.edu/multiwell/)4,5 and ab initio quantum calculations in the literature (see J. Phys. Chem. 1994, 98, 111; J. Phys. Chem. A 2005, 109, 4736; and Chemphyschem 2004, 5, 1864).6-8 The data are in, or very near, the low-pressure limit and therefore sensitive to the density of states of the excited ClONO and ClNO2 molecules as well as collisional energy transfer, centrifugal effects, and anharmonicity corrections. The data were underpredicted by a factor of 2.6 using accepted prescriptions for centrifugal corrections, collision frequency, and ignoring anharmonicity. The data could be fit by either making all rotational degrees of freedom active or artificially increasing the collision frequency, or maybe some of each. This last could also be complemented or supplemented by a multiplicative factor ascribed to anharmonicity.