Quenching of NCO(A2∑+) Radicals by Alkane Molecules

NCO radicals were produced by laser photolysis of CHBr3at 266 nm followed by the reaction of CH with N2O. The electronic ground state NCO radicals were electronically excited toA2Σ+(0000) state by laser irradiation at 438.6 nm. The quenching rate constants of NCO (A2Σ+) by CH4,n-C5H12,c-C6H12,n-C6H14, n-C7H16,n-C8H18were measured by investigating the time-resolved fluorescence from the excited NCO in room temperature (298 K). Removal was found to be very efficient where the rate constants with the above gases were measured as 2.35±0.14, 4.74±0.11, 4.65±0.12, 4.84±0.21, 5.15±0.19, 5.51±0.26, respectively, in units of 10~10 cm3/molec s. It is shown that the quenching rate constants and cross sections of NCO (A2Σ+) increase almost linearly with increasing the number of C-H bonds contained in the alkane molecules. By analysis, it is thought that chemical reactions play an important role in the quenching of the electronically excited NCO radicals and in addition to chemical reaction, collisional removal of NCO (A2Σ+) can take place via an E-V energy transfer.