請用此 Handle URI 來引用此文件:
http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/17545
標題: | 利用時域解析傅立葉轉換紅外光譜法研究乙醛與丙醛在248 nm之光分解反應 Photodissociation of Acetaldehyde and Propionaldehyde at 248 nm Detected by Time-resolved Fourier Transform Infrared Spectroscopy |
作者: | Kai-Chan Hung 洪楷展 |
指導教授: | 林金全 |
關鍵字: | 乙醛,丙醛,光分解,傅立葉轉換紅外光譜儀,漫遊機構,三體分裂, acetaldehyde,propionaldehyde,FTIR,roaming,triple fragmentation, |
出版年 : | 2013 |
學位: | 碩士 |
摘要: | 本論文使用時間解析傅立葉轉換紅外光譜儀偵測乙醛(與丙醛)分子於248 nm單光子能量之下,產生分子通道產物CO + CH4(與CO + C2H6)與自由基通道產物HCO + CH3(與HCO + C2H5)。加入焠熄氣體氬氣與分子碰撞會使得內轉移過程更有效率,因此增強產物的訊號。吾人在1900-2200 cm-1中紅外光範圍偵測到一氧化碳之基頻放光訊號,並且標定產物一氧化碳(1≦v≦9,J≦45)之振動轉動光譜譜線。藉由分析光解產物時間解析之振動及轉動分佈,我們得到丙醛光解產生的一氧化碳分子平均轉動能量為2.00±0.05 kcal/mol且平均振動能量為9.02±0.22 kcal/mol。在乙醛的結果中,我們認為會有部分甲醛基進行二次分解成CO,使得產物CO之轉動分佈為雙峰分佈,意即在一振動能階上會有兩組轉動溫度,其一溫度較低,另一溫度較高,特別在振動量子數為1時,低溫與高溫CO的比例為0.4:0.6。此現象說明著低溫CO由兩種來源所組成,其一為漫遊現象,另一為三體分裂,分別的比例由我們的308 nm實驗估計為<0.12與>0.28。而振動量子數為2時幾乎不發生漫遊現象,低溫的CO主要由三體分裂所產生(~0.15)。另外,乙醛光解產生的CO之平均轉動總能量為1.91±0.09 kcal/mol,平均振動總能量為8.34±0.45 kcal/mol。相較於乙醛的結果,光解丙醛產生的CO為單一波茲曼轉動分佈,說明丙醛可能不發生漫遊現象,推測原因可能立體效應(steric effect)所致。另外我們也沒有觀察到丙醛光解後來自三體分裂的CO,推測原因為大部分之剩餘能量分配至HCO的動能。藉由比較此兩分子在248 nm下的光分解反應,有助於我們對碳數不同的醛類分子於更高能量下有更進一步的了解。 Photodissociation dynamics of acetaldehyde (and propionaldehyde)at 248 nm was studied by detecting photofragments with step-scan time-resolved Fourier-transform infrared emission spectroscopy. We observed the molecular products CH4 + CO(C2H6 + CO) and radical products CHO + CH3(CHO + C2H5). The addition of Ar facilitates the collision-induced internal conversion which enhances the yields of fragments. The CO high resolution spectra indicate that the vibrational levels up to v=9 are populated and rotational levels up to J=45. In our results, the fragment CO from photolysis of propionaldehyde has the total rotational energy of 2.00±0.05 kcal/mol and the total vibrational energy of 9.02±0.22 kcal/mol. In the results of acetaldehyde, the HCO fragment is found to partially decompose to H and CO. The rotational population distribution of CO, especially at v=1, exhibits a bimodal feature. Both roaming mechanism and triple fragmentation contribute to the low-temperature component. According to our 308 nm result, their branching ratios are <0.12 and >0.28, respectively, while the high-temperature component is due to the conventional TS mechanism. The roaming pathway is hardly oberved at v=2, and almost all of the low-temperature component is attributed to triple fragmentation with a branching ratio of 0.15. Take the ratio into consideration, we obtain the total rotational energy of 1.91±0.09 kcal/mol and the total vibrational energy of 8.34±0.45 kcal/mol. However, the rotational population distribution of CO fragment from propionaldehyde can be fitted with only one Boltzmann function. The reason why we cannot observe the contribution of roamig mechanism and triple fragmentation may be ascribed to the steric effect and the partition of most of excess energy into the translational energy of HCO, respectively. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/17545 |
全文授權: | 未授權 |
顯示於系所單位: | 化學系 |
文件中的檔案:
檔案 | 大小 | 格式 | |
---|---|---|---|
ntu-102-1.pdf 目前未授權公開取用 | 7.85 MB | Adobe PDF |
系統中的文件,除了特別指名其著作權條款之外,均受到著作權保護,並且保留所有的權利。