目錄 第一章 緒論 1.1乙二醛之分子光譜..........................................1 1.2分解機制..................................................2 第二章 雷射實驗系統 2.1 乙二醛之合成............................................11 2.2 分子束真空腔體..........................................11 2.3 雷射系統................................................11 2.4 實驗程序................................................12 2.5 磁場裝置................................................13 第三章 理論 3.1光譜原理.................................................21 3.1.1 電子光譜..............................................21 3.1.2 轉動光譜..............................................21 3.1.3 原子核自旋能階........................................22 3.1.4 躍遷選擇律............................................23 3.2能量轉移式...............................................25 3.2.1小分子模式.............................................25 3.2.2 大分子模式............................................26 3.2.3 中間分子模式..........................................27 3.3齊曼效應.................................................28 第四章 實驗結果與分析 4.1轉動光譜.................................................36 4.2振動光譜.................................................38 4.3量子博動與螢光衰減.......................................41 4.3.1量子搏動分析...........................................41 4.3.2螢光雙自然指數衰減之分析...............................42 第五章 與 之交互作用 5.1 自旋軌道交互作用........................................76 5.2 二次電振自旋-軌道交互作用...............................78 5.3 之能階結構.............................................81 5.4 量子搏動之研究..........................................82 5.5 磁場效應................................................84 5.6能階密度分析.............................................87 第六章 乙二醛分解機制討論...................................99 第七章 結論.............................................103 參考文獻...................................................104 附錄一Main program (VB)....................................106 附錄二Results from analysis of quantum-beat patterns.......118 附錄三Gaussian biasing function............................126 附錄四Whitten-rabinovitch equation (Fortran)...............129 表目錄 TABLE. 1.1 Vibrational normal mode and frequencies of trans-glyoxal in its , , and states …………………………….7 TABLE. 2.1 Line positions（cm-1）of neon and uranium recorded with optogalvanic spectrometer…………………….……………...…………………….15 TABLE. 3.1 Character table of point group C2h……...…………………………….32 TABLE. 3.2 Symmetry species of JKaKc of trans-glyoxal in the C2h group……...…32 TABLE. 4.1 Rotational term values of the ground vibrational state of trans-glyoxal ( )………………………………………………………………..45 TABLE. 4.2 Observed and deviation from calculated line position (cm-1) of trans-glyoxal A band at origin 24 742.405 cm-1…..…..46 TABLE. 4.3 Observed and deviation from calculated line position (cm-1) of trans-glyoxal B band at origin 24 768.606 cm-1…....…47 TABLE. 4.4 Observed and deviation from calculated line position (cm-1) of trans-glyoxal C band at origin 24 782.173 cm-1………48 TABLE. 4.5 Observed and deviation from calculated line position (cm-1) of trans-glyoxal D band at origin 24 823.142 cm-1………49 TABLE. 4.6 Observed and deviation from calculated line position (cm-1) of trans-glyoxal E band at origin 24 833.702 cm-1………50 TABLE. 4.7 Observed and deviation from calculated line position (cm-1) of trans-glyoxal F band at origin 25 066.203 5 cm-1…….51 TABLE. 4.8 Observed and deviation from calculated line position (cm-1) of trans-glyoxal G band at origin 25 074.304 cm-1…........52 TABLE. 4.9 Observed and deviation from calculated line position (cm-1) of trans-glyoxal H band at origin 25 124.631 cm-1………53 TABLE. 4.10 Observed and deviation from calculated line position (cm-1) of trans-glyoxal I band at origin 25 129.295 2 cm-1……..54 TABLE. 4.11 Molecular constants for trans-glyoxal in its , and states and cis-glyoxl in its and states…..……………………… 56 TABLE. 4.12 Results from analysis of quantum-beat patterns……...…………….57 TABLE. 5.1 Matrix elements of spin-orbit operator. The elements are stated in term of quantum numbers J, K of singlet state…………………………….90 TABLE. 5.2 Selection rules and symmetry restriction of vibronic spin-orbit coupling between and states……………………………………….90 TABLE. 5.3 Molecular constants (cm-1) for trans-glyoxal it its excited triplet（ ）state....................................91 TABLE. 5.4 Hyperfine quantum beat frequencies, singlet-triplet coupling matrix elements, and gl factor centered at 22.98 and 27.74 MHz....................................................92 TABLE. 5.5 Density of states of , , and estimated using Whitten-Rabinovitch equation.................................92 TABLE. 6.1 Reaction enthalpies and barrier heights for glyoxal ....................................................101 圖目錄 FIG. 1.1 Conformation of glyoxal ( C2H2O2 )……………………………………….8 FIG. 1.2 Torsion potential of glyoxal…..……………………………………………9 FIG. 1.3 Transition state geometries for glyoxal dissociation optimized with method CBS-APNO for reaction, (a) C2H2O2®H2+2CO, (b) and (c) structures on the C2H2O2®HCO+HCO, (d) C2H2O2®H2CO+CO, and (e) C2H2O2® HCOH+CO……………………………………………………………...10 FIG. 2.1 Schematic diagram of experimental setup………………………………..16 FIG. 2.2 Optogalvanic spectra of Ne () and U (=) in the frequency range 23 700- 25 600 cm-1…..………….……………………………………..………..17 FIG. 2.3 Mutually orthogonal pump/detection geometry for LIF in the supersonic free jet expansion………………………………………………………..18 FIG. 2.4 Main program ( VB version )…………………………………………...19 FIG. 2.5 Plot of applied current vs. magnetic field measued by a gauss meter…...20 FIG. 3.1 Rotational energy levels of the ground electronic state（ ）of trans-glyoxal……………………………………………………………...33 FIG. 3.2 Schematic representation of coupling between the zero order bright state and the dark states and their corresponding emission decay trace. (a) small molecule. (b) intermediate case, and (c) statistical case……………….…34 FIG. 3.3 Splitting of energy levels in a magnetic field. A singlet level and a triple level are coupled by a spin-orbit interaction, giving rise to two eigenstates and . The dashed lines indicates the zeeman splitting in the absence of spin-orbit coupling………………………………………35 FIG. 4.1 Fluorescence excitation spectrum of of trans-glyoxal. The energy is relative to the origin of at 21 973.439 cm-1 and the assignments for the vibrational level in is shown..………………..59 FIG. 4.2 Rotationally resolved spectrum on branch RR1 of subband K' - K" = 2 - 1 ………………………….……………………………………………….60 FIG. 4.3 Rotationally resolved fluorescence excitation spectrum of glyoxal in the system for vibrational band A………………………………61 FIG. 4.4 Rotationally resolved fluorescence excitation spectrum of glyoxal in the system for vibrational bands B and C………………………62 FIG. 4.5 Rotationally resolved fluorescence excitation spectrum of glyoxal in the system for vibrational bands D and E……………………....63 FIG. 4.6 Rotationally resolved fluorescence excitation spectrum of glyoxal in the system for vibrational bands F and G………………………64 FIG. 4.7 Rotationally resolved fluorescence excitation spectrum of glyoxal in the system for vibrational bands H and I……………………….65 FIG. 4.8 (a)-(d) Quantum-beat patterns in the time resolved emission decay curves of glyoxal and the corresponding real-part of Fourier-transformed plots in frequency domain……………………………………………...66,67,68,69 FIG. 4.9 Fluorescence decay of glyoxal at various excitation wavelength.( in logarithmic scale )………………………………………………………..70 FIG. 4.10 Fluroescence excitation spectrum of glyoxal near frequency 25 450 cm-1. The rotational structure superimposed by some background signal indicates coupling to a large number of dark states……………..…….71 FIG. 4.11 Neff obtained from the ratio of amplitude fitted to the biexponential decay curves…..……………………………………………………………….72 FIG. 4.12 Fitted single exponential decay (=), fast ( ð ) and slow () time coefficients from fluorescence decay curve of glyoxal excited to …………………………………………………………………………..72 FIG. 4.13 Density of states estimated from fits to the biexponential decay curves..… …………………………………………………………………………..73 FIG. 4.14 Coupling matrix element ( ) obtained from analysis of quantum beat pattens and fits to the biexponential decay curve…………………..…...73 FIG. 4.15 Fluorescence decay of glyoxal detected at various excitation wavelengths. …………………………………………………………………………..74 FIG. 4.16 Plot of linewidth of quantum beat frequencies esimated from the fourier transform spectra. Symbol (o□□denotes the fwhm of beat frequency and (´□□the fwhm of line at zero....…….…………………………………….75 FIG. 5.1 Energy level diagram of hyperfine sublevels issued from possible NT = Ns , Ns ±1 levels coupled to a given Js = Ns. Triplets hyperfine energy splitting is given on the right……………………………………93 FIG. 5.2 (a) and (b) show time-resolved fluorescence decays of level 110 via RR0(0) transition of 61 vibrational band of propynal and (c) and (d) the corresponding Fourier-transform spectra. The decay were recorded with laser polarization parallel (a) and perpendicular (b) to the detector polarization (see text)…………………………………………………...94 FIG. 5.3 Fourier-transformed spectrum of fluorescence decay at various values of applied magnetic field on excitation RR0(2). denotes the polarization of laser and denotes the direction of external applied magnetic field ….……………………………………………………………………….95 FIG. 5.4 Plot of splitting of line centered at 50.78 , 27.74 , 22.98 MHz, as a function of the magnet field strength (see text)…………………………96 FIG. 5.5 Fourier transform of fluorescence decay of level 31 via RR0(2) transition for Ep^B. The insert is resulted from multiplying a gaussian function before fourier transform to reduce the line width.………………………97 FIG. 5.6 Intensity pattern of quantum beats resulted from multypling biasing function (a),(b) with simultation (c)-(f) in the frequency domain. The 31 fluorescence decay at 25254.36 cm-1 in an applied magnetic field of 3.4 G with laser polarization parallel (a, c, e) and perpendicular(b, d, f) to the direction of magnetic field. (c, d) without nuclear spin effect, (e, f) without nuclear spin(see text)………………………………………...…98 FIG. 6.1 Schematic energy diagram for dissociation of glyoxal……………...…102