Effectiveness of the scavenging action of NO in vacuum UV photolyses of C2H5Br: 121.6 - 193.1 nm region

Abstract

The radical scavenging effect of NO, in the system of C₂H₅Br photolyses in the vacuum UV region, has been studied as a function of the energy content of C₂H₅ radicals and of the irradiation time.

C₂H₆, one of the principal reaction products, from the primary radical process in the system can be completely suppressed by adding the appropriate amount of a radical scavenger, e.g. NO at greater than 0.1 Torr. However, by adding an unsuitable amount of NO, e.g. 0.02 Torr of NO and 50 Torr of C₂H₅Br, the reaction between the C₂H₅ radical and NO becomes competitive with that of the C₂H₅ radical and C₂H₅Br by the following mechanism:

where R represents the C₂H₅ or C₂H₄Br radical.

The competitive reaction ratio between the C₂H₅Br/C₂H₅ and NO/C₂H₅ systems was obtained as a function of the irradiation energies with the variation in irradiation time by observing the production of C₂H₆. The values of k_NO^I/k₁, deduced by comparing the observed and the theoretical values, were found to be 4.0 × 10³ at 121.6 nm, 9.5 × 10³ at 147 nm, 14.0 × 10³ at 163.3 nm, 17.0 × 10³ at 174.3 – 174.5 nm and 23.0 × 10³ at 193.1 nm.