利用時間解析傅立葉轉換紅外光譜法研究乙醛與甲酸甲酯在308/248 nm的光解反應: 漫遊機制 vs. 過渡態機制

Photodissociation of Acetaldehyde and Methyl Formate at 308 / 248 nm : Roaming vs. Transition State Mechanism Detected by Time-resolved Fourier Transform Infrared Spectroscopy

李厚寬(Hou-Kuan Li)

指導教授 ： 林金全

國立臺灣大學/理學院/化學研究所/碩士(2014年)

https://doi.org/10.6342/NTU.2014.01174

摘要

自從2004年甲醛的光分解反應中被報導存在漫遊機制(roaming mechanism)
後這個主題的論文就如雨後春筍般的被發表，如乙醛(CH3CHO)、丙醛
(C2H5CHO)、甲酸甲酯(HCOOCH3)等都被發現有漫遊機制的蹤跡。他們觀察到在
H2+CO這個分子通道，CO有雙轉動分布(bi-rotational distribution)，且隨著偵測轉動態的不同，兩個分布所貢獻的比例也不同，其中低轉動態的CO對應到的是一個非常低的移能。後來，經由半古典軌跡(quasi-classical trajectory)的計算也證實了如果經由ㄧ般
的途徑(過渡態機制)形成分子產物H2+CO，其CO會有較高的轉動態及移動能分
布。
本論文使用時間解析傅立葉轉換紅外光譜法研究乙醛與甲酸甲酯在308nm / 248nm下的光分解反應。其中，甲酸甲酯的研究我們有跟義大利佩魯賈大學prof. Aquilanti的研究團隊合作。在CH3OH+CO這個分子通道中，我們藉由取得1900-2200cm-1範圍的CO高解析(0.25cm-1)圖譜，並且配合光譜模擬來分析CO的內能分布。我們發現，在CO分子中v=1及2的振動態存在著雙轉動分布，我們排除其他通道產生CO的可能，並請prof. Aquilanti團隊執行半古典軌跡的計算，發現實驗與計算的結果相當吻合。而在乙醛的實驗中，我們得到CO在v=1的漫遊機制與過渡態機制的分支比，漫遊機制佔0.10

關鍵字

傅立葉轉換紅外光譜 ； 光分解 ； 乙醛 ； 甲酸甲酯 ； 漫遊機制

並列摘要

Since roaming mechanism have been reported in photolysis of formaldehyde at 2004, the papers on this topic have been published mushroomed, such as acetaldehyde (CH3CHO), propionaldehyde (C2H5CHO), methyl formate (HCOOCH3 ) etc. were found to have traces of the roaming mechanism. CO were found to be bi- rotational distribution and with the detection of different rotational states, the proportion contributed by the two mechanism are different. The low-J component of CO are correlated to a very low translational energy. Later, the quasi-classical trajectory calculations also confirmed that the conventional transition state mechanism to form molecular products H2 + CO, CO will have higher angular momentum and with substantial translational energy released.
We use time-resolved Fourier transform infrared spectroscopy to study photolysis reaction of acetaldehyde and methyl formate at 308nm / 248nm. In project of methyl formate, we collaborate with prof. Aquilanti research team in Perugia university in Italy. We obtain the range of 1900-2200cm-1 CO high-resolution (0.25cm-1) spectrum to analyze the internal energy of CO and with the aid of spectral simulation We found that the CO molecule in v = 1 and 2 are bi-rotational distribution. Prof. Aquilanti team perform quasi-classical trajectory calculations, and the experimental results and calculations are quite consistent. In acetaldehyde experiments, we got branching ratio of roaming mechanism in v=1 is 0.10±0.02. Compare to Kable’s LIF results of 0.13, which represents that the time-resolved Fourier transform infrared spectroscopy is a promising method to observe roaming reaction in the internal energy aspect.

並列關鍵字

TR-FTIR ； photodissociation ； acetaldehyde ； methyl formate ； roaming

參考文獻

[1] A. Suits, Acc. Chem. Res. 41, 873( 2008).

Zhang, J. Rheinecker, L. B. Harding, and J. M. Bowman, science 306, 1158 (2004).

[8] S. A. Lahankar, S. D. Chambreau, X. Zhang, J. M. Bowman, and A. G. Suits, J. Chem. Phys. 126, 044314 (2007).

[9] X. Zhang, J. L. Rheinecker, and J. M. Bowman, J. Chem. Phys. 122, 114313 (2005).

[10] J. L. Rheinecker, X. Zhang, and J. M. Bowman, Mol. Phys. 103, 1067 (2005).