Isotope effects in the quenching of electronically excited atoms. Part 3.—Quenching of I(52P½) by HD

Abstract

Spin-orbit relaxation of I(5²P_½) by HD has been investigated using time-resolved atomic absorption spectrophotometry. The thermally averaged cross-section for relaxation by HD has been determined as (2.1 ± 0.3)× 10^–18 cm²(at 293 K), which is three times larger than the cross-section for H₂ and which in turn in 92 times greater than that for D₂. The results strongly suggest that energy transfer proceeds via resonant processes involving electronic → vibration + rotation energy exchange. Isotope effects observed in the quenching of Tl(6²P_3/2) and Te(5³P_1,0) are also discussed and it is proposed that “selection” or “propensity” rules control the changes in rotational state and that long range multipolar coupling may be involved when resonant transfer is possible. Tentative values for a number of single channel cross-sections are presented.