利用六極柱對於空間中方位化的 (S)-1溴-2-甲基丁烷以及 (R)-3-溴樟腦進行光分解的分子動力學之研究以及利用六極柱對甲酸甲酯分子進行能階選擇之漫遊機制的模擬研究

Abstract

此論文分為三部分，第一以及第二分別為 (S)-1-溴-2-甲基丁烷以及 (R)-3溴樟腦在方位化下的條件進行光分解反應，並透過離子影像判斷產生之光分解碎片之向量關聯；三為模擬在光分解方位化的甲酸甲酯分子來探討漫遊機制。在此研究中，我們開發了一套時間切片離子影像結合六極柱能階選擇器之實驗系統，並針對兩實驗個別需求進行些微改裝。藉由此系統所產生之光分解碎片的離子影像可以用來探討多原子分子在光分解反應中複雜的向量關聯性。在第一個以及第二個實驗中，我們分別將 (S)-1-溴-2-甲基丁烷以及 (R)-3-溴樟腦通過加熱系統而產生之氣體分子導入脈衝閥中產生分子束，再藉由六極柱對氣體分子進行方位化，在光分解之後，通過分析獲得的Br以及Br* 離子影像，我們可以得出anisotropy parameter、離子的能量分布以及速率分布。同時，在調整極化光方向之後，我們可以得出光分解過程中永久偶極矩、過渡偶極矩以及離子飛行方向這三個向量的關聯性。此外也討論了在光分解掌性化合物過程中，無法從離子影像分辨出不同掌性化合物的原因。第三部分的研究為模擬利用2+1共振增強多光子離子化在230奈米中解離能階選擇後之甲酸甲酯分子，並且獲得CO(v=0)的離子影像，其中可以分辨出轉動能階在low-J的離子由光分解走漫遊機制所產生，另外轉動能階在high-J的離子則由經傳統的過渡態理論所產生。其中由low-J以及high-J所產生的比率可以用來和未經過方位化的甲酸甲酯分子所光分解而產生CO的比率來進行比較。進而得知六極柱進行方位化影響反應路徑的不同。

This thesis is divided into three parts: I. Photodissociation of oriented (S)-1-bromo-2-methylbutane and study the stereodynamics from the ion image of photogragments. II. Photodissociation of oriented (R)-3-bromocamphor and study the stereodynamics from the ion image of photogragments. III. Roaming pathway determination by simulating the photodissociation of oriented methyl formate. In these research, we developed an experimental system which included the time-of-flight spectroscopy coupled with ion imaging and combined with hexapole state selector. Besides, we slightly improved the system based on the requirement of these two research. The ion image of photofragments was applied to realize the complicated vector correlation of polyatomic during photodissociation. In the first and second research, we induced (S)-1-bromo-2-methylbutane and the (R)-3-bromocamphor into the heating system to produce vapor and conducted it into pulsed valve, respectively. The hexapole would interact with the molecular beam to carry out the orientation of molecule. After the photodissociation, we analyzed the ion image of Br and Br* to obtain the anisotropy parameters, speed distributions and kinetic energy distributions. Furthermore, when we adjusted the polarization of laser in an appropriate degree, we could study the correlations between permanent dipole moment, transition dipole moment and recoil velocity. In addition, we also discussed the reason on the failure in chiral discrimination of enantiomer during the photodissociation. In the third research, we tried to simulate the application of (2+1) resonance-enhanced multiphoton ionization (REMPI) following photolysis of state-selected methyl formate at 230 nm and obtained the ion image of CO (v=0). The low-J and high-J components of bimodal rotational distributions are ascribed to roaming pathway and conventional transition state pathway, respectively. The hexapole plays the role to interfere the branching ratio of low-J and high-J components.