乙硫基與氧分子之平衡及C2H5SO2與二氧化氮之反應動力學研究

Abstract

本實驗利用雷射光解－雷射誘發螢光法(Laser Photolysis－Laser Induced Fluorescence)研究C2H5S與O2之平衡反應以及其中間產物C2H5SO2與二氧化氮(NO2)的反應動力學。 C2H5S＋O2＋M → C2H5SO2＋M (1) C2H5SO2＋NO2 → Products (2) 實驗以波長248 nm的雷射光光解二乙基二硫醚(C2H5SSC2H5)，產生乙硫基後，再以一波長為410.3 nm的雷射光將乙硫基激發至電子激發態，經由激發態乙硫基分子放出之螢光強度對時間變化情形求得反應速率常數值。實驗是控制在[O2]0>>[C2H5S]0之條件，使反應在擬一級(pseudo first－order)狀況下進行。 在實驗溫度範圍228 K至258 K間，可觀察到平衡反應(1)的發生，其平衡常數值為(1.59－15.40) ×10-18 cm3 molecule-1，在不同的光解雷射能量與不同實驗壓力(80－180 torr)下得到的結果，顯示平衡常數值與雷射能量及系統壓力無相依性。 當系統中加入NO2後，可觀察到其與平衡反應產物C2H5SO2反應。而隨著溫度的降低，反應速率有些微增加之趨勢。 我們測得反應(2)在234 K－254 K之阿瑞尼士表示式(Arrhenius equation)為： k2(T)＝(4.88±1.35) ×10-12 exp[(886±219)/T] cm3 molecule-1 s-1

A Laser Photolysis—Laser Induced Fluorescence (LP—LIF) system has been used to study the reaction kinetics of the equilibrium between C2H5S and O2 and the reaction of C2H5SO2 with NO2 at 223－258 K, and 50－200 torr of total pressure.C2H5S radicals were produced by photolyzing C2H5SSC2H5 molecules with an excimer laser output at 248 nm.The concentration of C2H5S radicals was monitored at 410.3 nm with an excimer-pumped dye laser. We observed bi-exponential decay of C2H5S in the presence of O2 which implied an equilibrium between them.The equilibrium constants were determined at temperatures 228－258 K, Keq(T)＝(1.44±0.35) ×10－27 exp[(5325±512)/T] cm3 molecule－1.The rate constant of C2H5SO2 with NO2 was also derived as k2(T)＝(4.88±1.35) ×10－12 exp [(886±219)/T] cm3 molecule-1 s-1 at 234－254 K.