Quenching of I*(2P1/2) by atomic and molecular hydrogen and halogens

Abstract

A new experimental method has been devised by which it is possible to study the deactivation of I*(5 ²P_1/2) by radical atoms as well as by stable molecular species. A small, steady-state concentration of I atoms is generated in a discharge–flow system, and then a fraction of these atoms is directly excited using the output from a pulsed iodine-atom, photochemical laser. The subsequent decay of I*(5 ²P_1/2) is observed by monitoring the I₂(B→X) emission, the B[³Π(0⁺_u)] state of I₂ being formed by recombination, I*+ I + M → I₂(B)+ M. The following quenching rate constants (cm³ molecule^–1 s^–1) at room temperature have been determined: k_H2=(1.03 ± 0.06)× 10^–13, k_Br2=(5.5 ± 0.1)× 10^–11, k_Cl2⩽ 5 × 10^–14, k_H=(4 ± 2)× 10^–14, k_I⩽ 5 × 10^–13, k_Br=(5.1 ± 1.9)× 10^–13 and k_Cl=(2 ± 1)× 10^–11.