Collisional quenching of excited iodine atoms (5p5 2P1/2) by Cl2 in a flow system

Abstract

Quenching and reactions of laserexcited I(52 P 1/2) atoms with halogen and interhalogen molecules J. Chem. Phys. 69, 641 (1978); 10.1063/1.436629Collisional quenching of excited iodine atoms I(5p 5 2 P 1/2) by selected molecules Time-resolved infrared emission from photolytically generated I*ep 1/2) has been studied in a slow flow apparatus. The total rate of deactivation ofI*e P 1/2) by Cl 2 has been measured to be no more than 8X 10-15 cm 3 molecule-I S-I, substantially slower than previous reports. Evidence is presented for a very fast (k =2 X 10-10 cm 3 molecule-I S-I) relaxation of 1* by Cl atoms, which can account for both the earlier and the present observations.

Quenching of I(2P1/2) by Cl2 and Cl Atoms over the Temperature Range 297−663 K

“…Burrows 4 and De Juan and Smith 5 reported rate constants of 1.5 × 10 -11 and (2(1) × 10 -11 cm 3 s -1 , respectively. Hall et al 6 estimated that the rate constant could be as high as 2 × 10 -10 cm 3 s -1 , but the lower values are generally accepted. In contrast, room-temperature quenching of I* by Cl 2 is slow to the point where it is difficult to determine the rate constant 4,6,7 .…”

“…Hall et al 6 estimated that the rate constant could be as high as 2 × 10 -10 cm 3 s -1 , but the lower values are generally accepted. In contrast, room-temperature quenching of I* by Cl 2 is slow to the point where it is difficult to determine the rate constant 4,6,7 . Early measurements 3,2 that involved photolytic generation of I* in the presence of Cl 2 were complicated by co-photolysis of Cl 2 , followed by rapid I* + Cl quenching.…”

“…Early measurements 3,2 that involved photolytic generation of I* in the presence of Cl 2 were complicated by co-photolysis of Cl 2 , followed by rapid I* + Cl quenching. Burrows 4 and Hall et al 6 made careful studies of this problem using pulsed laser photolysis of CF 3 I (or C 3 F 7 I)/ Cl 2 mixtures. Burrows 4 obtained a Cl 2 quenching rate constant of (2.0(0.1) × 10 -14 , whereas Hall et al 6 gave an upper bound of <8 × 10 -15 cm 3 s -1 .…”

“…Burrows 4 and Hall et al 6 made careful studies of this problem using pulsed laser photolysis of CF 3 I (or C 3 F 7 I)/ Cl 2 mixtures. Burrows 4 obtained a Cl 2 quenching rate constant of (2.0(0.1) × 10 -14 , whereas Hall et al 6 gave an upper bound of <8 × 10 -15 cm 3 s -1 . Discharge flow methods were also used to examine I* + Cl 2 .…”

“…ICl is an efficient quencher of I* (k ) 2 × 10 -11 cm 3 s -1 ), 4,7 so the presence of small concentrations of ICl was an additional complication for both the photolysis and discharge flow experiments. In the analysis of the former, it was suggested 6 that some ICl originated from a slow pre-reaction between CF 3 I and Cl 2 . Secondary photochemical reactions contributed a much faster time dependent component to the ICl concentration.…”