臺灣博碩士論文加值系統

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.

摘要 i
Abstract ii
圖目錄 vi
表目錄 x
第一章 緒論 1
第一節 大氣化學 1
第二節 醯鹵光分解反應 2
第三節 草醯氯的光解反應動態學 3
第四節 氯分子偵測的相關研究 4
第二章 氯分子光譜 6
第一節 氯分子光譜的譜線位置 6
A. 電子態 6
B. 振動態 8
C. 轉動態 8
D. 譜線位置與躍遷選擇律 9
第二節 氯分子光譜的譜線強度 11
A. 能階的居量分布 12
B. 核自旋統計比重 12
C. 同位素效應 14
D. 躍遷偶極矩、法蘭克－康敦因子與霍爾－倫敦因子 14
第三章 腔體震盪光譜法 17
第一節 吸收光譜的原理 17
第二節 腔體震盪光譜法基本原理 18
第三節 腔體震盪光譜法的靈敏度 23
A. 方法一 23
B. 方法二 24
第四節 腔體震盪光譜法的誤差來源 25
A. 高反射率鏡子(high-reflectivity mirror) 25
B. 雷射模態(laser modes) 26
C. 雷射雜擾/散粒雜訊(shot noise) 27
D. 雷射帶寬 28
E. 干涉效應(interference effect) 28
第四章 實驗架設與訊號處理 30
第一節 腔體震盪光譜法 30
第二節 實驗儀器與藥品 31
A. 高反射鏡 31
B. 摻釹釔鋁石榴石雷射 32
C. 染料雷射 33
D. 雷射染料 34
E. 準分子雷射(excimer laser) 36
F. 光電倍增管(photomultiplier tube, PMT) 37
G. 數位示波器 38
H. 時序控制器 39
I. 藥品 41
J. 壓力計 42
K. 機械幫浦 43
L. 氣態紫外光－可見光吸收光譜儀 44
第三節 數據處理 45
A. 腔體震盪光譜法 45
B. 氣態吸收截面積 48
第五章 結果與討論 49
第一節 草醯氯在248 nm下的吸收截面積 49
第二節 草醯氯的光解光譜 51
第三節 光解產物的振動分布 54
A. 光譜模擬 55
B. 氯分子的振動分布 57
第四節 預測草醯氯的光解通道 62
A. 能量相關實驗 62
B. 壓力相關實驗 64
C. 氯原子的再結合 66
第五節 草醯氯的光解量子產率 68
A. 直接定量法 68
B. 間接定量法 71
C. 量子產率的修正 72
D. 自由基清除實驗 76
第六節 雷射誘導螢光與自我淬熄常數 78
第七節 光分解路徑 84
A. 溫度對分子解離通道的影響 84
B. 文獻回顧 85
C. 光解路徑 85
結論 88
參考資料 89

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