甲硫基與臭氧反應機構之研究

Abstract

本研究是利用雷射光解 -雷射誘發瑩光法(Laser-Photolysis/Laser-Induced Fluoresence)測量CH3S自由基與臭氧之反應動力學。我們先以波長193nm的雷射光解甲硫醚和甲硫醇製造CH3S，在反應進行的時間內再以波長371nm之雷射光激發甲硫基，以測量其誘發瑩光而定量之。甲硫酸光解後可能會製造許多種不同的自由基而產生旁反應 (side reaction)，使得化學反應趨向複雜。與前人所做的實驗結果相符(33)。本研究觀察到CH3S有再生的現象，當系統中加入2-5 Torr的O2後，此CH3S的再生現象即消失，主要的原因是由於CH3S與O3，甲硫醚之間的一連串反應 CH3SCH3+hv(193nm) → CH3S+CH3 (1) CH3 + O3/ CH3SCH3 →→ CH3S (2) 加 入 O2後 CH3+O2 → CH3O → CH3S (3) 由於此化學反應機構至今仍不甚清楚，因而引發了我們對本研究的興趣。我們利用模擬軟體去模擬可能的反應情況。經由模擬之情況與實驗的結果相比較去建立一個反應機構，以此來幫助我們了解所進行的化學反應。在模擬的過程中我們了解到CH3，氧原子和氫原子部扮演了相當重要的角色。光解後產生的CH3會跟臭氧生成CH3O。氧原子也會去跟甲硫醚反應生成OH，而氫原子會與臭氧反應生成OH。CH3O與OH均在本實驗中以雷射誘發螢光法測得。

A laser photolysis-laser induced fluorescence system has been used to study the reaction kinetics of CH3S radical with O3. The CH3S radicals were produced by photolyzing CH3SCH3 molecules with an excirner laser output at 193nm .The concentration, of CH3S was monitored with the output of an excimer-pumped dye laser at 371nm. This measurements showed that the title reaction proceeds rapidly. Non-exponential profiles of CH3S3 were observed and addition of O2 scavenge the regeneration. OH and CH3O radicals were detected in our system via LIF method. The time profiles of [OH] and [CH3O] were recorded under various experiment conditions, which showed that these two species were produced in secondary reactions. Methyl (CH3) radical is believed to play an crucial role in the regeneration of CH3S. We attempted to resolve the reaction mechanism with the aid of a computer software FACSIMILE, and the results were discussed.