STATISTICAL SIMULATION OF IF ANGLE AND ANGLE-VELOCITY DISTRIBUTIONS FROM THE CROSSED-BEAM REACTION F-2-]IF+I(I)

The angular distributions and angle-velocity distributions for the IF product molecule from the reaction F+I-2-->IF+I have been computed for the conditions of the study by Firth et al. ( 1988, 1989): crossed mo lecular 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 simulat ion. This is probably the first accurate calculation of an angle-veloc ity distribution for a crossed-beam experiment. All essential features of the reaction can be explained assuming the [IFI] collision interm ediate to be a long-lived complex, with a reaction cross section of ap proximately 30 Angstrom(2). The average fraction in final translationa l energy f(t) is approximately 30%, while most of the energy, 40%, end s up in vibration. The main parameter influencing the results is the r otational temperature T-rot of the iodine molecule, which is not accur ately known from experiment. The best fit is found at T-rot= 15 K. The re is, at the present state of experiments, no need to assume that the reaction is comprised of two different channels: one direct short-liv ed and one long-lived, as done in other studies. The vibrational and r otational distributions will be fully treated in a forthcoming publica tion applying the same model to vibrationally and rotationally resolve d results. It is argued that the old standard procedures used to trans form and interpret crossed beam data should not be used, since they ma y give rise to erroneous conclusions due to the non-inclusion of angul ar momenta and angle-velocity couplings.