烷烃类分子对NCO(A^2Σ^+)自由基的猝灭

Quenching of NCO( A~ 2Σ^+) Radicals by Alkane Molecules

采用激光光解 激光诱导荧光 (LP LIF)的方法 ,用 2 6 6nm激光光解CHBr3 分子产生CH自由基 ,再与N2 O继续反应作为NCO自由基的产生源 ,用 4 38.6nm激光将电子基态X 2 Πi(0 0 10 )的NCO激励到激发态A2 Σ+ (0 0 0 0 )上 ,通过检测激发态NCO时间分辨荧光信号 ,测得室温 (2 98K)下NCO(A2Σ+ )被烷烃类分子猝灭的实验结果 ,获得了A 2Σ+ (0 0 0 0 )态猝灭速率常数 .实验发现 ,随着烷烃分子中C -H键数增加 ,其猝灭截面也近线性增加 ,但随着分子体积增大 ,这种增加趋缓 .

NCO radicals were produced by laser photolysis of CHBr 3 at 266 nm followed by the reaction of CH with N 2O. The electronic ground state NCO radicals were electronically excited to A 2Σ +(00 00) state by laser irradiation at 438.6 nm. The quenching rate constants of NCO ( A 2Σ +) by CH 4, n C 5H 12 , c C 6H 12 , n C 6H 14 , n C 7H 16 , n C 8H 18 were 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 cm 3/molec s. It is shown that the quenching rate constants and cross sections of NCO ( A 2Σ +) 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 ( A 2Σ +) can take place via an E-V energy transfer.