Reaction with Propane of I(5²P_1/2), produced by Photolysis of Iodine in the Continuum of the B³∏_ou⁺–X¹Σ_g⁺ System, and by Collisional Release inside the Banded Region

Abstract

FROM an analysis of the kinetics of the formation of i-propyl iodide in irradiated mixtures of iodine and propane, we have recently shown that electronic excitation of atomic iodine to the 5²P_1/2 state greatly enhances its chemical reactivity; in respect of hydrogen atom abstraction (activation energy ∼ 5 kcal/mole) its behaviour is similar to that of atomic chlorine. The B³∏_ou⁺–X¹Σ_g⁺ electronic transition of iodine exhibits a banded region with a convergence limit at 4995 Å, and a continuum at shorter wave-lengths¹. Dissociation of molecular iodine in the continuum produces one atom in the 5²P_3/2 ground state and one atom with the 5²P_1/2 spin-orbit orientation corresponding to an excitation energy of 21.7 kcal/mole. The occurrence of I(5²P_1/2) reactions has been established by a study of the inhibition caused by addition of various species which deactivate I(5²P_1/2) to the ground state: There is a general correspondence between efficiencies measured directly by flash spectroscopy^2,3 and those determined from the isopropyl iodide inhibition. The production of I(5²P_1/2) also occurs well inside the banded region above 4995 Å collisional release resulting from long-range attractive interaction with any added gas, and the kinetic energy available during collision, effectively shifts the continuum threshold to longer wave-lengths.