利用步進式時域解析傅式轉換紅外光譜法研究2-溴丙醯氯之光分解反應

Photodissociation of 2-Bromopropionyl Chloride Detected with Time-resolved Fourier Transform Infrared

劉佳雲(Chia-Yun Liu)

指導教授 ： 林金全

國立臺灣大學/理學院/化學研究所/碩士(2010年)

https://doi.org/10.6342/NTU.2010.10686

摘要

本論文係以步進式時間解析-傅立葉轉換光譜儀，研究CH3CHBrCOCl 分子與淬熄氣體Ar 於248nm 波段下之光解反應，並利用光分解產物的特徵放光，探討可能的光分解機制。在氣態情況下觀測光分解產物，可得到一系列HCl (1≤v≤ 3, J≤ 13),HBr (v= 1, J≤ 9)和CO (1≤v≤ 3, J≤ 36)振動-轉動譜線，並分析光解之初生產物的振動、轉動分布情形及內能分配。此外，以Br2及CH4 捕捉CH3CHBrCOCl 分子在光解過程中產生的Cl 自由基，分析實驗結果顯示碰撞誘發內轉換(Internal Conversion,IC)過程，再進行解離而產生光分解產物為主要通道。其光分解反應解離機制為在電子基態(S0)的CH3CHBrCOCl 氣態分子，吸收單一248 nm 雷射光子能量躍遷至第一電子激發態(S1)，經由Ar 進行內轉換(Internal Conversion, IC)過程，激發態CH3CHBrCOCl 分子以非放光躍遷(Radiationless transition)形式轉換至高內能的電子基態(S0)，含有高內能的CH3CHBrCOCl 分子其能量高於反應能障，分裂生成HCl，HBr 與CO 等光分解產物。

關鍵字

傅立葉光譜儀 ； 光分解反應 ； 2-溴丙醯氯

並列摘要

By employing time-resolved Fourier-transform infrared emission spectroscopy, the fragments of HCl(v=1-3), HBr(v=1), and CO(v=1-3) are detected in one-photon dissociation of 2-bromopropionyl chloride (CH3CHBrCOCl) at 248 nm. The Ar gas is added to induce internal conversion and enhance the fragment yields. The time-dependent high-resolution spectra of HCl and CO are analyzed to determine the corresponding ro-vibrational energy deposition of 9.96±0.22 and 7.44±0.57 kcal/mol, respectively, while the rotational energy in HBr is evaluated to be 0.93±0.11kcal/mol. As a Boltzmann population distribution is assumed, the branching ratio of HCl/HBr yield is estimated to be 1:0.53, in agreement with the calculated ratio of dissociation rate constants. The measurements involving an active reagent of Br2 suggest that the probability of HCl contribution from a hot Cl reaction with the precursor be negligible. The HCl elimination channel under the Ar addition is verified to be slower by two orders of magnitude than the Cl elimination channel. With the aid of ab initio calculations, the observed fragments are proposed to dissociate on the hot ground state CH3CHBrCOCl. A two-body dissociation channel is favored leading to either HCl +
CH3CBrCO or HBr +CH2CCOCl, in which the CH3CBrCO moeity may further undergo secondary dissociation to release CO.

並列關鍵字

FTIR ； Photodissociation ； CH3CHBrCOCl

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