Multi-pathway I 2 dissociation model for COIL

Abstract

Vibrationally excited iodine I₂(X,v>20) is an important intermediate in the standard COIL dissociation model. This intermediate is populated by the I* + I₂(X) reaction. In this model excitation probabilities for the v-th I₂(X) vibrational level &gamma;(v) are critical parameters. In the present study we examined excitation probabilities &gamma;(v) based on the comparison of calculated populations of vibrational levels of iodine molecules with their experimental values. The total excitation probability for I₂(X, v>25) was found to be &gamma;(v>25)&asymp; 0.1. The standard dissociation model with &gamma;(v>25) &asymp;0.1 cannot provide the observed dissociation rates. Moreover the number of O₂(a) molecules consumed per dissociated I₂ molecule would exceed 20 if the standard dissociation model is the predominant dissociation pathway, which is at variance with experiment. Barnault et al.3 found that the populations of I₂(10&le;v&le;23) were much higher than &nu;&ge;30. Such high populations of I₂(10&le;v&le;23) could be explained by means of direct excitation in the I* + I₂(X) reaction. A satisfactory agreement between calculated I₂(v) populations and the experimental data was achieved for the total excitation probability &gamma;(v>25) =0.05-0.1 and for &gamma;(15<v<25) =0.8-0.9. The results of computer calculations utilizing the multi pathway model are in good agreement with experimental iodine dissociation rates.