氰氧基與乙烯及乙烷之反應動力學研究

Abstract

本實驗使用雷射光解/雷射誘發螢光法在不同溫度及壓力下偵測氰氧基 (NCO)與乙烯(C2H4)及乙烷(C2H6)的反應速率常數值.在NCO與C2H4的反應 中有高能的複合物(complex)產生,因此其反應速率常數可能與壓力有關. 我們將在定溫(298K)下研究其反應速率常數對壓力(10 -413 torr(He))的 相依性,以及在定壓(10torr,200torr)下研究其反應速率常數隨溫 度(246-473K,298-473K)而變化的情形.在溫度298K,壓力413torr時我們可 得其反應速率常數之高壓極限(high pressure limit)為: k1=5.55*10 ^-12 cm^3 molecule^-1 s^-1在壓力10torr時我們可將其反應速率常數與 溫度之關係可表為: k2=3.42*10^-8*T^-1.61*exp(-82.2/T) cm^3 molecule^-1 s^-1在壓力200torr時我們可將其反應速率常數與溫度之關 係可表為: k3=1.34*10^-8*T^-1.40*exp(4.45/T) cm^3 molecule^-1 s^-1 NCO+C2H6 為一抓氫(hydrogen abstraction)反應,其反應可表為下 式: NCO+C2H6--->HNCO+C2H5其反應速率常數與壓力無關.我們在定溫(298 K),定壓(53torr)下測得其反應速率常數值為 k=1.82*10^-14 cm^3 molecule^-1 s^-1. Absolute rate coefficients for the reactions of NCO radical with C2H4 and C2H6 were determined by using laser photolysis/ laser induced fluorescence technique. We used He and N2 as buffer gases . We measured the rate coefficients for the reaction of NCO radical with C2H4 in the pressure range between 10 torr and 413 torr at 298K,and in the temperature range from 246K to 473K at a total pressure of 10 torr, and from 298K to 473K at a total pressure of 200 torr. The result were expressed as: NCO+C2H4--->products k1=5.55*10^-12 cm^3 molecule^-1 s^-1 (high pressure limit) at a total pressure of 10 torr k2( T)=3.42*10^-8*T^-1.61*exp(-82.2/T) cm^3 molecule^-1 s^-1 at a total pressure of 200 torr k3(T)=1.34*10^-8*T^-1.40*exp(4.45/T) cm^3 molecule^-1 s^-1 The rate coefficient for the reaction of NCO radical with C2H6 was determined as 1.82*10^-14 cm^3 molecule^-1 s^-1 at 298 K at 53 torr.