Sarkar : Competitive Energy Dynamics in Irmpd of Uf

The photochemica l iso tope separation sche mes have renewed the detailed in vestigati ons o f gas phase photophys ics and photochem istry of UF6 . O ne of the schemes is based o n massive multiphoton excitation o f UF6 us ing o ne or more suitab le IR laser frequcncy in 16l-lm region in its ground electronic state. In the present work we have mode lled such Infrared Multiphoton Di ssoc iati on (IRMPD) on a rate equation formali sm. Using RRKM theory, the mult iphoton di ssociati on rate constants for UF6 wi th 16 ~lJn laser have been es timated. It is shown that about 50 laser photo ns, which are 15 photons excess over the d issoc iation th reshold of 3 eV, are req uired fo r dissoc iation of each UF6 mo lecule. Using the present model, the nuencc dependence of di ssociati on y ie ld has been evaluated and it is fo und that MPD of UF6 occurs with a threshold tluence of I 1.2 J cm-. Isotopic selecti vity in thi s model is desc ribed as the diffe rence in the rate of lase r energy absorpti on for the two isotopi c spec ies. Considering vario us time scales in volving exc itation, colli sio nal deac ti vat ion and li fe ti me o f e nergized 235UF6 molecul e, the ex tent of selec ti vity loss has been estimated.