A theoretical investigation of the vacuum UV photolysis of carbon suboxide with trifluoromethane

Abstract

In this dissertation, the vacuum-UV photolysis of C302 in thepresence of CHF3 at 1470 AO has theoretically been investigated with theintent to predict the main photolysis products.As already known, the primary photochemical products of the shortwavelengthphotolysis of C302 are free carbon atoms. Of the three atomicstates of carbon produced, C(lO) atoms react with CHF3 present through insertioninto the C-H bond to produce vibrationally excited C2HF! molecule.This excited molecule, with a calculated energy content of about 158 kcal,either collides with other molecules present and stabilizes or decomposesthrough a-a or a-B HF elimination to give difluorovinylidene, :C2F2, ordifluorocetylene, C2F2 as the major products.In an attempt to distinguish between the two decomposition reactionsof the excited C2HF! molecule, the specific rate constants have beenevaluated by means of the RRKM Theory of unimolecular reactions. Twomodels have been developed for the a-a transition state complex, whereasthe geometric parameters for the a-B complex have been calculated throughthe use of the modified Semi-Ion Pa.ir Theory of four-centered reactions.The calculations have been carried out for four critical energy values;81, 90, 94 and 100 kcal.As a result, it has been found out that both of the decompositionreactions occur during the photolysis of C302/CHF3 system. However, a-aelimination reaction is the predominant one. It may be concluded that outof 100 C2HF~ molecules decomposing, 68 molecules decompose through a-aelimination of HF and yield difluorovinylidene, while 32 molecules decomposeby a-S elimination and produce difluoroacetylene.The stabilization/dissociation ratio has also been calculated asa function of pressure with the assumption that the non-equilibrium energydistribution of C2HFj molecules may be presented by the Gaussian Distributionfunction. The effects of pressure, critical energy values and of thetransition state models have been examined. Finally, the relative concentrationsof the main photolysis products have been calculated over thepressure range of interest.As a conclusion, a reaction mechanism, consistent with the resultsobtained, has been proposed ..