林金全臺灣大學：化學研究所李維斌Lee, Wei-BinWei-BinLee2007-11-262018-07-102007-11-262018-07-102007http://ntur.lib.ntu.edu.tw//handle/246246/51728摘要 在本論文中，描述了我們如何自行建造一組實驗系統，以及針對碘化氰分子與其雙聚物光分解的研究。這套裝置結合了飛行時間質譜儀(Time-of-flight mass spectroscopy, TOF MASS) 與共振多光子游離法 (resonance-enhance multi photon ionization, REMPI)， 以及離子速度成像偵測 (velocity map image，VELMI) 等技術，用以解析並研究光解離反應中反應物與產物的不同能態間的關係。其中離子速度成像技術 (VELMI) 的引用，更是提升了我們對產物速度的解析能力並且獲得更精確的產物角度分佈。 我們在277 nm, 266nm, 248nm 的波長光解碘化氰分子，並且運用共振多光子游離法選擇要離化的基態 (I≡2P3/2) 或激發態 (I≡2P1/2) 碘原子。在上述波長所測得的碘原子產量的分支比 (I*/I branching ratio) 分別為 0.75 ± 0.02，1.22 ± 0.02，和 0.85 ± 0.1。基態碘原子產生的主要分佈中，其各向異性參數(anisotropic parameter，β) 在上述波長分別為1.25 ± 0.05, 1.31 ± 0.05, and 0.96 ± 0.05。激發態碘原子的主要分佈中，其各向異性參數則分別為1.66 ± 0.1, 1.78 ± 0.1, and 1.86 ± 0.1。這強烈顯示了，在我們的實驗波長範圍中，光分解的初生態主要來自3Π0+ 能態的平行躍遷。 參考其他的文獻，在上述的實驗波長，光分解過程中產生的基態或激發態碘原子，伴隨出現的產物CN經常是處於電子基態 (X2Σ+) 以及振動基態 (v”=0) 的能態，然而其轉動能態則有較大的差異。伴隨基態碘原子產生的CN(X2Σ+ ，v”=0)處於非常高的狀態 (N=0-60) 。伴隨激發態碘原子產生的CN(X2Σ+ ，v”=0) 轉動能態則小的多(N<30)。我們的實驗在266 nm 的波長下，有高達0.76的產率來自平行躍遷。這值介於Houston 等人實驗所得的0.85 以及Morokuma研究室所計算的0.66。顯示我們的實驗結果能符合其他實驗機構的結果。 我們也利用離子速度成像技術 (VELMI) ，來研究碘化氰雙聚物的光分解。在研究過程中，發現有中性的碘分子，因此我們偵測到的碘離子，來源可能是碘分子及其分子離子。為了確定我們訊號的來源。我們對照了以純粹碘分子作為樣品的實驗來釐清反應的機制，發現碘化氰雙聚物光解過程中，的確產生了多量的中性碘分子。我們也同時以理論計算的方式，從雙聚物的幾何形狀與基態位能來討論碘化氰雙聚物光解產生碘分子的機制。 關鍵字：碘化氰；光分解；離子速度成像；共振多光子游離；動態學。Abstract The photodissociation experiments of ICN and (ICN)2 are carried out with a home-built system. The state selected reactants and products can be investigated by using time-of-flight (TOF) mass spectroscopy coupled with resonance-enhanced multiphoton ionization (REMPI) techniques. A velocity map imaging (VELMI) detection is implemented to analyze speed and angular distributions of fragments in a high energy resolution. Jet-cooled ICN molecules have been photodissociated at 277, 266, and 248 nm. Both ground state I (I≡2P3/2) and spin-orbital excited I* (I≡2P1/2) are detected by [2+1] REMPI, respectively. The corresponding branching ratio of I/I* is determined to be 0.75 ± 0.02, 1.22 ± 0.02, and 0.85 ± 0.1. The product anisotropic parameter, β, of I and I* are also obtained. For the main distribution of I products, β is estimated to be 1.25 ± 0.05, 1.31 ± 0.05, and 0.96 ± 0.05. For the main distribution of I* products, β is estimated to be 1.66 ± 0.1, 1.78 ± 0.1, and 1.86 ± 0.1. This strongly suggested that the ICN photodissociation at this range mainly result from the 3Π0+ parallel transition. In the mean time, the products with high internal energy are also observed. By considering previous results, I is mainly accompanied with the CN (X2Σ+) fragments in v”=0 at hot rotational temperature, whereas I* is produced with CN (X2Σ+) in v”=0 state but with cold rotational temperature. No hot vibrational CN fragment is observed at this VI wavelength range studied. At 266 nm the observed parallel transition ratio is 0.76. This value lies in between 0.85, reported by Houston et al, and 0.66, calculated by Morokuma et al. We also investigated photodissociation of ICN dimer under jet-cooled condition using velocity map imaging technique. Because the neutral I2 molecules have been observed in the ICN dimer experiment, I+ was expected to originate from the photodissociation of neutral I2 or I2+. After carrying out the photodissociation experiment of I2+ ions via 2+1 REMPI from pure I2 sample, the total reaction pathways of ICN dimer photodissociation have been found. We also carried out the theoretical calculations to predict the geometry and energies of ground state and excited state of ICN dimer.Contents Acknowledgements…………………………………………………....I Chinese Abstract……………………………………………………III Abstract……………………………………………….....…......V Contents................................................VII Figure Captions……………………………………………………...X Table Captions……………………………………………………XIII Chapter 1 Introduction of Ion Image System……………………………..1 1-1 Introduction…………………….………………………………1 Chapter 2 Experimental Sections……………………………………...…..9 2-1 Experimental Methods………………………………….………....9 2-1-a Photodissociation and ionization……………….……….…10 2-1-b VELMI Newton sphere projection……….………….…..14 2-1-c Ion image accumulation…………………………….……16 2-1-d 2-D image and 3-D velocity distribution transformation...17 2-2 Experimental Setups………………………………………...……20 VIII 2-3 System Velocity calibration………………………………………24 2-3-1 Velocity calibrated by O2 photodissociation……………….24 2-3-2 Velocity calibrated by Br2 photodissociation………………26 2-3-3 Velocity calibrated by I2 photodissociation………………...27 Chapter 3 ICN A-band Photodissociation Detection by Velocity Mapping Image……………………………………………………….…40 3-1 Introduction…………………………………….………………...40 3-2 Experimental Setup………………………………………………46 3-3 Results……………………………………………………………48 3-3-1. TOF Mass Spectra…………………………………………48 3-3-2. Images and Corresponding Speed, Angular, and Energy Distributions………………………………………………...……48 3-3-3. Relative Quantum Yields………………………………….51 3-4 Discussion......................................................................................54 3-5 Conclusion......................................................................................64 IX Chapter 4 ICN Dimer Photodissociation…………………………………74 4-1 Introduction………………………………………………………74 4-2 Experiment……………………………………………………….77 4-3 Results……………………………………………………………79 4-3-1 Photodissociation of (ICN)2 near 266nm…….…………79 4-3-2 Photodissociation of I2……………………………….…..82 4-4 Discussion…………………………………………………….….84 4-4-1 Hot I+ ions…………………………………………….……84 4-4-2 Geometry of (ICN)2………………………………………..85 4-5 Conclusion……………………………………………………….88 Chapter 5 References…………………………...……………………...…98 5-1 References of Chapter 1……………………………….………..98 5-2 References of Chapter 2……………………………….………..101 5-1 References of Chapter 3……………………………….………..102 5-1 References of Chapter 4……………………………….………..105 X Figure Captions Figure 2-1 A: The imaging approach for measuring Newton spheres from photodissociation………………..………………………28 Figure 2-2. Angular distribution photofragment dissociation in laboratory frame…...……………………………………………………29 Figure 2-3. Angular distribution photofragment dissociation in molecular frame…………………………………………..........30 Figure 2-4. Possible routes for fragment ions formation…………..31 Figure 2-5. The variables for optimizing the ion lens geometry…..32 Figure 2-6. Best simulation of the Ion Lens……………………….33 Figure 2-7. The home-made REMPI state selected VELMI system design…………………………………………………………..33 Figure 2-8. The ion lens assembly. The dimensions of this assembly are calculated by the SIMIOM 7.0 program……………………….34 Figure 2-9. The design of differential wall……………………………...35 Figure 2-10, The Speed distribution of O2 at 225nm after the inverse BASEX translation…………………………………………….36 Figure 2-11, The Speed distribution of O2 at 225nm after the inverse BASEX translation. The Voltage is (1200, 811, 0) for (Repeller, Extractor, Ground)……………………………………………….36 XI Figure 2-12. The images of O2 at 225nm……………………………….37 Figure 2-13. The Speed distribution of O2 at 225nm………………….37 Figure 2-14. The images and the speed distribution of Br2 dissociation at 267nm………………………………………………………….38 Figure 2-15. The images and the speed distribution of I2 dissociation at 266nm…………………………………………………….…….39 Figure 3-1 Time-of-flight mass spectrum of ICN obtained at 266nm..67 Figure 3-2 Ion velocity mapping images of I (a, c, e) and I*…...68 Figure 3-3 Speed distribution of I and I* fragments………………69 Figure 3-4 ICN center-of-mass translational energy distribution and angular distribution at 266nm…………………………………..70 Figure 3-5. The total internal energy distribution of ICN photo- dissociation at 266nm…………………………………………..71 Figure 3-6. The ICN A-Band absorption spectrum……………..72 Figure 3-7. The relative Quantum yield at 266nm…………………73 Figure 4-1. Velocity map imaging of ICN monomer at 266nm, (a) I excited state, (b) I ground state……………………………….89 XII Figure 4-2. Velocity map imaging of pure I2 at 266nm………...90 Figure 4-3. The REMPI spectra of ICN from 264.5 nm to 270.5 nm..………………………………………………………..……91 Figure 4-4 Time-of-flight mass of fragments from photodissociation of (ICN)2 in supersonic beam………………………………..…….92 Figure 4-5 The power dependence of the integrals of I+ and I2+ on laser pulse energy…………………………………………..………93 Figure 4-6 Raw image of I+ of (ICN)2 and corresponding speed distributions of I+, obtained under clustering conditions……………………………………………..……….94 Figure 4-7 The kinetic energy distribution and anisotropy parameter of photodissociation of I2+ at 266.417nm………….………..……95 Figure 4-8 The energy scheme of possible channels of I2+ photodissociation at λ=266.42nm…………………………………….....96 Figure 4-9 The calculated ground state structure of ICN dimmer…....97 XIII Table Captions Table 3-1. Anisotropic Parameters β in Different Cannels…….……….65 Table 3-2. The Quantum Yields of I* at ICN Dissociation Channels Φ(I*)……………………………………..…………………….65 Table 3-3. The relative Quantum Yields in Different Wavelengths……..66 Table 3-4. Initially 3Π0 Fraction and Curve-Crossing Probability……...661696132 bytesapplication/pdfen-US碘化氰光分解離子速度成像共振多光子游離動態學Cyanogen IodideICNphotodissociation dynamicsvelocity map ion imageREMPIthesishttp://ntur.lib.ntu.edu.tw/bitstream/246246/51728/1/ntu-96-D89223028-1.pdf