266 nm雷射光解溴仿之放射光譜;266 nm Photolysis of Bromoform

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题名:	266 nm雷射光解溴仿之放射光譜;266 nm Photolysis of Bromoform
作者:	陳政仲;Cheng-Chung Chen
贡献者:	化學研究所
日期:	2006-06-12
上传时间:	2009-09-22 10:16:09 (UTC+8)
出版者:	國立中央大學圖書館
摘要:	溴仿分子光解後產生的溴原子對臭氧層的破壞是人類必須嚴重正視的問題，而且主要光解的光源是來自於長於真空紫外光波長的光線。在有關溴仿光解的文獻中，以266 nm為光解光源的研究至今尚未對於光解的反應機制有一個定論。本次實驗分別於「超音速自由噴射裝置」（supersonic free jet）以及「流動樣品槽」（flow cell）內，使用266 nm雷射光解溴仿分子，搭配有較高靈敏度的增強式偶合電荷裝置（intensified charge-coupled device, ICCD）當偵測器，成功取得光解後高訊雜比的放射光譜。經由計算各物種的能階資訊，參考相關的文獻，以及利用同位素取代方法（CDBr3）來驗證在放光光譜得到的譜帶訊號。所發現的物種放光，包括直接光解產生的CH (A2Δ → X2Π) 、CH (B2Σ- → X2Π)，光解溴仿首次發現的CH (C2Σ+ → X2Π) 和Br原子譜線，以及兩個CH碰撞產生的C2 (d3Πg → a3Πu) 和可能由兩個激發態Br碰撞產生的Br2 (b3Π0u+ → X1Σg+)；其中更進一步地證明CH (C) 以及激發態Br皆可能為吸收三個光子過程的產物，且激發態Br的產生較不可能是經由碰撞而來。最後可順利地推論出光解溴仿可能的三光子連續反應機構，並探討可能之數種反應途徑。 Atmospheric bromine atoms mainly come from the photolysis of bromoform and play a crucial role in the ozone depletion. In the previous studies of the bromoform photolysis, the reaction mechanism is controversial and is still unclear thus far. This study aims to clarify the photolysis mechanism of bromoform at 266 nm. The photolysis was observed in a supersonic free jet expansion as well as in a slow flow cell. Nascent emission spectra were successfully acquired with an intensified charge-coupled device. In the emission spectra, several species include CH (A2Δ → X2Π), CH (B2Σ- → X2Π), CH (C2Σ+ → X2Π), Br atomic transition, C2 (d3Πg → a3Πu) and Br2 (b3Π0u+ → X1Σg+) were observed. Among these species, CH(C) and the excited Br are firstly detected in the photolysis of bromoform. The excited C2 results from the collisions between the electronically excited CH and the excited Br2 most likely comes from the collisions between two excited Br atoms. The power-dependence experiments indicate that both of CH (C) and the excited Br are likely the products of a three-photon process. It is proved by the pressure-dependence experiment that the excited Br does not result from the collisions. We have therefore deduced the mechanism of the 266 nm photolysis of bromoform.
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