烷烃和胺类分子对电子激发态CH(A^2Δ和B^2Σ^-)自由基猝灭

Quenching of CH(A,B) Radicals by Alkane and Amine Molecules

用266nm激光光解CHBr_3分子产生CH(A,B)态自由基,通过测量CH(A,B→X)自发辐射的时间分辨信号测定室温下(CH_3)_2NH、(C_2H_5)_2NH、(C_2H_5)_3N、n-C_5H_(12)、n-C_6H_(14)和n-C_7H_(16)对CH(A,B,v'=0)的猝灭速率常数.发现猝灭速率常数与猝灭剂烷烃分子中的C-H键数近似成线性关系,但对大的烷烃分子,这种增加逐渐趋缓.用碰撞络合物模型计算胺类分子及烷烃分子与CH形成碰撞络合物时的生成截面,结果表明,在电子激发态CH自由基的猝灭过程中,碰撞对子间的多极相互吸引势和色散力作用势可能起重要作用.

The measurements of quenching rate constants of CH(A,B) radicals by (CH3)2NH, (C2H5)2NH, (C2H5)3N, n-C5H12, n-C6H14 and n-C7H16 are presented by using laser photolysis of CHBr3 at 266 nm and time-resolved fluorescence quenching technique. It is found that the quenching rate constants for both A and B states increase almost linearly with increasing C-H number contained in the alkane molecule. But for larger alkane molecules, it appears that the quenching rate increase is smaller than that for small alkane molecules. The formation cross sections of complexes between electronically excited CH and amine and alkane molecules were calculated by using collision complex model. It is found that the dependence of the formation cross section of complex on the number of C-H bonds in the alkane molecules is in good agreement with that of the measured quenching cross section. This implies that the attractive forces between CH (A and B) and alkane molecules are probably important in collisional quenching processes of CH (A and B) by alkane molecules. The similar conclusion could be drawn for quenching of CH(A and B) by amine molecules.