林金全臺灣大學：化學研究所魏佩瑩Wei, Pei-YingPei-YingWei2007-11-262018-07-102007-11-262018-07-102006http://ntur.lib.ntu.edu.tw//handle/246246/51868腔體振盪吸收光譜法(Cavity Ring-down Spectroscopy)技術是近年來發展迅速的一種測量吸收光譜的新方法，其震盪腔體是由兩片在特定波段下具有極高反射率的鏡子(反射率通常為99.9%以上)所組成，當雷射光進入腔體會在腔體中來回震盪直到雷射光的強度衰減到幾乎為零，我們在示波器上會看到雷射光強度對時間呈現一指數衰減的圖，當雷射光頻率與待測分子(Br2)之能態躍遷共振時，雷射光的衰減加速，我們可以偵測到雷射光在腔體震盪的時間，以雷射光的衰減速率對雷射波長做圖即可得到Br2的吸收光譜。 我們利用pump-probe研究二溴甲烷(CH2Br2)及一溴二氯甲烷(CHClBr2)在被248nm光分解後，溴分子的量子產率及初生態的振動分佈，進而探討Br2生成的機制。在過去的研究中，大部分的研究團隊看到的為最主要的解離通道為解離一個溴原子，而我們利用腔體震盪吸收光譜法，成功的偵測到溴分子的解離通道，更有搭配理論計算去證實產生溴分子的這個解離通道確實可能發生。Cavity Ring-down Spectroscopy (CRDS) is a relatively new direct absorption technique and its applications are developed very quickly in recently years. The method is based on measurement of the decay rate of a pulse light trapped in an optical cavity which is formed by a pair of highly reflective(R>99.9%) mirrors. A plot of decay rate as a function of laser frequency gives the absorption spectrum. We used a pump-probe technique to study of nascent vibrational distribution and the quantum yield of Br2 following photodissociation of CH2Br2 and CHBr2Cl and then we can deduce two possible photodissociation mechanisms for CH2Br2 and CHBr2Cl to product Br2. Moreover, the results agree with a given theoretical calculation.Contents Acknowledgments..........................................IV Chinese Abstract……………………………………………………VI Abstract……………………………………………………………VII Figure Captions……………………………………………………VIII Chapter 1 Introduction of Cavity Ring-down spectroscopy (CRDS)…1 1-1 Principles of Cavity Ring-down spectroscopy………1 1-2 Data Analysis for CRDS…………………………………3 1-3 CRDS: History and Development………………………8 1-4 Sensitivity of CRDS……………………………………11 1-4-1 Theoretical Treatment…………………………………11 1-4-2 Factors that influence the sensitivity of CRDS……14 References……………………………………………………………24 Chapter 2 Vibrational distribution of Br2 following photodissociation of CH2Br2 ……………………………………26 2-1 Introduction…………………………………………26 2-1-1 The transitions of halogens in visible and near infrared region………………………………………………29 2-1-2 The absorption spectrum of pure Br2…………31 2-2 Experiment……………………………………………32 2-2-1 Experimental Setup………………………………32 2-2-2 Theoretical methods………………………………34 A. Ab initio electronic structure calculations…34 B. RRKM rate constant calculations…………………35 2-3 Results and Discussions……………………………35 2-3-1 Nascent vibrational distribution of Br2 fragment………35 2-3-2 Quantum yield for Br2 elimination……………38 2-3-3 Reaction pathways of Br2 following the photodissociation of CH2Br2.…………………………………41 2-4 Conclusions……………………………………………46 References……………………………………………………………68 Chapter 3 Vibrational distribution of Br2 following photodissociation of CHBr2Cl……………………………………74 3-1 Introduction and Experimental section………74 3-1-1 Theoretical methods………………………………75 A. Ab initio electronic structure calculations…75 B. RRKM rate constant calculations…………………76 3-2 Results and Discussions…………………………76 3-2-1 Nascent vibrational distribution of Br2 fragment……76 3-2-2 Quantum yield for Br2 elimination…………77 3-2-3 Reaction pathways of Br2 following photodissociation of CHBr2Cl……………………………………78 3-3 Conclusions…………………………………………81 References…………………………………………………………941578414 bytesapplication/pdfen-US腔體振盪吸收光譜法Cavity Ring-down Spectroscopythesishttp://ntur.lib.ntu.edu.tw/bitstream/246246/51868/1/ntu-95-R93223005-1.pdf