Statistical simulation of IF angle and angle—velocity distributions from the crossed beam reaction F+I2→IF+I

Abstract

The angular distributions and angle—velocity distributions for the IF product molecule from the reaction F+I2→IF+I have been computed for the conditions of the study by Firth et al. (1988, 1989): crossed molecular beams at relative kinetic energy of approximately 40 kJ mol−1. The RRKM-SA program called UNIMOL is used to statistically simulate the experiment with all its details. Good agreement is found for both types of distributions, using vibrational quantization in the simulation. This is probably the first accurate calculation of an angle—velocity distribution for a crossed-beam experiment. All essential features of the reaction can be explained assuming the [IFI*] collision intermediate to be a long-lived complex, with a reaction cross section of approximately 30 Å2. The average fraction in final translational energy ft is approximately 30%, while most of the energy, 40%, ends up in vibration. The main parameter influencing the results is the rotational temperature Trot of the iodine molecule, which is not accurately known from experiment. The best fit is found at Trot=15 K. There is, at the present state of experiments, no need to assume that the reaction is comprised of two different channels: one direct short-lived and one long-lived, as done in other studies. The vibrational and rotational distributions will be fully treated in a forthcoming publication applying the same model to vibrationally and rotationally resolved results. It is argued that the old standard procedures used to transform and interpret crossed beam data should not be used, since they may give rise to erroneous conclusions due to the non-inclusion of angular momenta and angle—velocity couplings.