Topic I：Rotational and vibrational energy transfer effect of CH B2Σ-(v’=1) Topic II：Vibrational distribution of Br2 molecule following photo-dissociation of bromine containing molecules by using cavity ring down absorption spectroscopy.

這本論文主要分成兩個各自獨立的部分，每一部分都包含二章。 在第一部分的第一章介紹了一些光譜及傅立葉轉換紅外線光譜法的背景知識。在第一部分的第二章，研究CH 2Σ- (v’=1)自由基在與Ar, CO, 和N2O碰撞後的振動及轉動能量轉移的效應。我們用激發-偵測的技術來研究振動及轉動能量轉移速率。我們得到轉動能量轉移速率普遍大於振動能量轉移速率；轉動能量轉移速率的數量級在10-10 ~ 10-11 cm3 molecule-1 s-1 之間，而振動能量轉移速率的數量級在10-11 ~10-12 cm3 molecule-1 s-1 之間。我們發現對振動能量轉移速率而言，它和轉動量子數是無關的；轉動能量轉移方面，對CH 2Σ- (v’=1)自由基，我們發現在一次碰撞的情況下，會有多量子(multi-quantum)轉移的情況發生。大致上來說，振動及轉動能量轉移的速率，是N2O > CO > Ar，我們認為是多原子效應(polyatomic effect)及永久偶極矩(permanent dipole)所造成的。 在第二部分的第一章，我們介紹了腔體振盪吸收光譜法(CRDAS)的基本原理。在第二部分的第二章，我們成左漣Q用腔體振盪吸收光譜法得到純的溴分子的連續吸收截面積(continuous absorption cross section)。接著，我們研究溴仿(CHBr3)及二溴甲烷(CH2Br2)在被248nm光分解後，溴分子的量子產率及初生態的振動分布。在過去的研究中，大部分的研究團隊都認為最主要的光分解通道為解離一個溴原子；但我們利用腔體振盪吸收光譜法，成它a偵測到了另一個光分解的通道：溴分子的解離通道。我們得到溴分子的量子產率分別為0.23±0.05及0.26±0.07。；另一方面我們發現在溴仿光分解後所得到的溴分子是屬於熱振動的分布(vibrational-hot distribution)。我們認為這種光分解所得的溴分子處於熱振動的分布，是來自於三溴甲烷或二溴甲烷吸收248 nm後，從激發的電子能態(excited electronic states)經由內轉換(internal conversion)和高振動態的電子基態(highly vibrational levels of ground state)偶合，進而分解成產物。我們亦有搭配理論計算從能量的觀點去証實產生溴分子的這個解離通道確實可以發生。Part I In this thesis, it will be separated into two individual parts: part I and part II. Each part has two chapters. In the chapter 1 of part I, some basic background of spectroscopy and Fourier transform infrared method is illustrated. And in the chapter 2 of part I, the fine state-resolved rotational and vibrational energy transfer of CH B2Σ- (v’=1, N) by collisions with Ar, CO, and N2O is illustrated. It is the first time to observe the rotational energy transfer and vibrational energy transfer processes of a specific fine state for B 2Σ- (v’=1) of CH radical. We use pump-probe technique to determine RET and VET rate constants of CH B (v’ = 1, 0≦ N ≦ 6) with collisions of Ar, CO, and N2O. The RET is anticipated to be larger than VET for each collider. The determined RET rate constants range from 10-11 to 10-10 cm3 molecule-1 s-1, while the determined VET rate constants range from 10-12 to 10-11 cm3 molecule-1 s-1. The relative values of RET and VET rate constants are consistent with the results founded by Cooper and Whitehead. The findings of multi-quantum changing within single collision suggest that the collisions possibly dominated by the long-range attractive force. The k’VET shows no rotational quantum number dependence for these three quenching gases. This conclusion is the same as the results reported previously by Crosley et al. and Whitehead et al. The kVET of N2O is three times larger than that of CO and nine times larger than that of Ar, respectively. This result is related to polyatomic effect, permanent dipole moment, and inefficient vibration-translation transfer. The number of internal degrees of freedom of N2O is larger than that of CO and Ar, therefore N2O can remove more energy than CO and Ar within single collision. In other words, N2O is more efficient than CO and Ar. Polyatomic effect and permanent dipole moment play a role in vibration and rotational energy transfer process. Part II In the chapter 1 of part II, the basic working principle of cavity ring-down absorption spectroscopy (CRDAS) is introduced. In the first section in the chapter 2 of part II, the total continuous absorption which includes A – X, B – X, and C – X transition of pure diatomic bromine is obtained by using CRDAS. In the second section, the primary photodissociation channels of CHBr3 and CH2Br2 which is ignored in the past studies have been investigated. CHBr3 + hν -->Contents Acknowledgments..................................................................................IV Chinese Abstract………………………………………………………VI Abstract………………………………………………………………VIII Figure Captions…………………………………………………………X Table Captions……………………………………………………….XVI Part I Chapter 1 Fundamental Theory……………………………………………………..1 1.1 Fundamental principles of molecular spectroscopy………....................2 1.1.1 Diatomic molecules…………………………………………………..2 (1) Hund’s coupling case (a)……………………………………………6 (2) Hund’s coupling case (b)……………………………………………8 (3) Hund’s coupling case (c)…………………………………………...10 (4) Hund’s coupling case (d)…………………………………………..11 1.1.2 Selection rules……………………………………………......................15 1.2 The principles of step-scan Fourier transform infrared spectrometer…………………………………………………………………..17 1.2.1 Introduction…………………………………………………………...17 1.2.2 Basic theory and instrument of Fourier transform spectrometer…………………………………………………………..19 1.2.2.1 Michelson interferometer……………………………………..20 1.2.2.2 Mathematical Manipulation of Fourier Transform …………………………………………………………………..22 1.2.2.3 The effect of sampling frequency on the resultant spectrum………………………………………………………26 1.2.2.4 Apodization function…………………………………………..30 1.2.2.5 Step scan………………………………………………………..31 References…………………………………………………………………………...34 Chapter 2 Investigation of RET and VET for CHB2Σ- (v’=1) radical……...........36 2.1 Introduction & Motivation…………………………………………………36 2.2 Experimental Section……………………………………………………….43 2.2.1 Vibrational energy transfer (VET)…………………………………..43 2.2.1.1 Experimental Setup……………………………………………43 2.2.1.2 Kinetic model…………………………………………………..48 2.2.1.3 Results………………………………………………………….49 2.2.1.4 Summary of VET………………………………………………60 2.2.2 Rotational energy transfer (RET)…………………………………....61 2.2.2.1Experimental Setup…………………………………………….61 2.2.2.2Kinetic model…………………………………………………...65 2.2.2.3 Results………………………………………………………….66 2.2.2.4 Summary of RET……………………………………………...74 2.3 Conclusions and Discussion of VET and RET………………………..…...74 2.3.1 Vibrational energy transfer…………………………………..………74 2.3.2 Rotational energy transfer…………………………………………....76 2.3.3Comparison of VET and RET………………………………………...82 2.4 Conclusion…………………………………………………..……………….83 References…………………………………………………………………………...85 Part II Chapter 1 Cavity Ring Down Absorption Technique……………………………..88 1.1 Introduction…………………………………………………………..……..88 1.2 The Principle of Cavity-Ring Down spectroscopy…………………..…….91 1.3 Cavity Stability……………………………………………………………...96 1.4 Sensitivity of CRDS………………………………………………………..100 1.4.1 Theoretical Treatment………………………………………………...100 1.4.2 Factors which affect CRDS sensitivity………………………………102 (a) Laser Pulse Noise………………………………………………………103 (b) Laser bandwidth………………………………………….....................103 (c) Interference effects in CRDS………………………………………….105 (d) Laser transverse modes……………………………………………….106 (e) Cavity Mirrors…………………………………………………………106 References…………………………………………………………………...……..108 Chapter 2 Vibrational distribution of Br2 following photodissociation of multi-bromine atoms containing molecules by using cavity ring down absorption spectroscopy………………………………………………………………………..110 2.1 Introduction………………………………………………..………………110 2.2 The transitions of halogens in visible and near infrared region…………………………………………………………………….111 2.3 Experiment…………………………………………………………………116 2.3.1 The absorption spectrum of Br2……………………………….……..116 2.3.1.1 Experimental Setup…………………………………………..117 2.3.1.2 Results and Discussions……………………………………...123 2.3.1.3 Summary……………………………………………………...130 2.3.2 Investigation of Br2 produced from photolysis of CHBr3……..……..131 2.3.2.1 Introduction and Experimental Section………..…….131 2.3.2.2 Potential Energy Calculation……………………………..136 2.3.2.3 Results and Discussions…………………………………...137 2.3.2.4 Conclusions………………………………………………...156 2.3.3 Investigation of Br2 fragment produced from photodissociation of CH2Br2…………………………………………………………………...158 2.3.3.1 Introduction and Experimental section…………………..158 2.3.3.2 Results and Discussions…………………………………...159 2.3.3.3 Conclusions………………………………………………...16