Kinetics of photophysical and photochemical processes involving selective excitation of ortho-I 2 by laser radiation

Abstract

A method is described for studying elementary processes in an ortho-para iodine molecular mixture during selective excitation of ortho-I 2 and direct fluorescent control of the concentration of para-I 2 and ortho-I 2 molecules. Selective predissociation of ortho-I 2 molecules was carried out with argon laser radiation. It is shown that the conversion of para-I 2 into ortho-I 2 proceeds under formation of the complex I 3. The rate constants of elementary processes have been evaluated: the probability of iodine atom recombination on the cell walls, δ=(1.04±0.07)×10 4s −1; the desorption probability, K *=(2.30±0.25)×10 −4s −1; the conversion rate constant, β=(1.88=0.09)×10 16 cm 6 mol −2 s −1; the quantum yield of predissociation from the excited state B 3Π o+u( u=43) of I 2 molecules, γ=1.66×10 −5. The selective photochemical reaction of electronically excited iodine molecules with 2-hexene has been investigated. When the mixture (iodine-40 mtorr, 2-hexene - 2 torr) was irradiated for 10-12 min by the 5145 Å line of an argon laser with a power of 2.2 W, photochemical separation of ortho- and para-modifications of iodine was realized with the enrichment coefficient being equal to 4.