理學院: 化學研究所指導教授: 林金全黃挺剛Huang, Ting-KangTing-KangHuang2017-03-022018-07-102017-03-022018-07-102016http://ntur.lib.ntu.edu.tw//handle/246246/272125腔體震盪光譜法(Cavity ring-down spectroscopy, CRDS)是一項具有極高靈敏度的吸收光譜技術。CRDS使用兩端為一對高反射鏡的腔體，使雷射光在腔體內震盪，並量測雷射光的衰減速率，計算出震盪生命期，使用震盪生命期的倒數對雷射光波長作圖即可得到吸收光譜。我們使用準分子雷射(excimer laser)產生波長248 nm的紫外光以光解草醯氯(oxalyl chloride)，再使用CRDS來偵測氯分子的離去通道。藉由能量相關實驗，可以得知氯分子的產生為一單光子反應。藉由壓力相關實驗，可以得知光解總反應為一級反應，而非來自氯分子的再結合，也進一步以乙醯氯的光解實驗排除再結合之可能性。利用光譜模擬來分析氯分子在基態的振動分支比為1 : (0.12 ± 0.03) : (0.011 ± 0.003)，是屬於較熱的振動態，對應的振動溫度為360 ± 60 K。利用紫外光可見光光譜儀測得草醯氯在248 nm下氣態吸收截面積為2.78 × 10-19 cm^2，搭配CRDS量測結果可以計算出量子產率為0.8 ± 0.4。藉由速率模擬，可以推測在同樣條件下二次反應對於氯分子生成的貢獻約為17~27 %。在高壓條件下，草醯氯容易與系統中其他分子碰撞，造成淬熄，使氯分子生成減少。利用雷射誘導螢光技術進行的激發態生命期實驗亦可佐證淬熄效應。Cavity ring-down spectroscopy is an ultra-sensitive absorption spectroscopy technique. It is based on measurement of the decay rate of a pulsed laser light trapped in an optical cavity with a pair of highly-reflective mirrors. The plot of decay rate as a function of laser wavelength gives the absorption spectrum. Using CRDS, we detect the Cl_2 B^3 Π_(0+u) ← X^1 Σ_(g+) absorption transition from the molecular elimination channel following 248 nm photolysis of oxalyl chloride. Energy-dependence experiments show that Cl_2 elimination is a one-photon process. Pressure-dependence experiments show that the reaction is first-order overall. Comparing the experimental spectrum with the simulated spectrum, we can obtain the branching ratio of Cl_2 vibrational levels, which is 1 : (0.12 ± 0.03) : (0.011 ± 0.003). The branching ratio corresponds to a vibrational temperature of 360 ± 60 K, indicating the Cl_2 formed is vibrationally hot. Using a modified UV-Vis spectrophotometer, we measure the absorption cross-section of oxalyl chloride at 248 nm to be 2.78 × 10-19 cm^2, and further calculate the quantum yield of Cl_2 formation to be 0.8 ± 0.4. Kinetic modelling shows that secondary reactions could contribute to 17~27 % of the Cl_2 signal detected. At high pressures, excited oxalyl chloride is quenched because of collisions, which causes the quantum yield of Cl_2 to decrease. The self-quenching effect is also supported by laser-induced fluorescence (LIF) measurements.4607574 bytesapplication/pdf論文公開時間: 2018/8/26論文使用權限: 同意有償授權(權利金給回饋學校)腔體震盪光譜法光分解氯分子草醯氯CRDSCavity ring-down spectroscopychlorine moleculeoxalyl chloridethesis10.6342/NTU201601655http://ntur.lib.ntu.edu.tw/bitstream/246246/272125/1/ntu-105-R03223117-1.pdf