腔體震盪光譜法於乙二醯二溴的光分解研究

Abstract

腔體震盪光譜法是一項新的吸收光譜技術，此方法是利用量測穿透過一對高反射率鏡面所組成的腔體的雷射光衰減速率，將雷射光頻率對衰減速率做圖，即可得到吸收光譜。由於它擁有高靈敏度、架設簡單…等優點，因此成為在氣態微量分析上良好的工具。在本篇論文中，我們使用248 nm的準分子雷射光解乙二醯二溴分子，利用CRDS的技術偵測溴分子 的吸收躍遷來觀看產生溴分子的離去通道。藉由能量相依和壓力相依的實驗驗證我們觀測到的溴分子係由乙二醯二溴吸收單一光子的解離過程。我們從溴分子 的躍遷吸收光譜圖，去分析溴分子在基態的振動分支比，獲得1:0.65±0.09:0.34±0.07 ，這表示我們觀測到的溴分子是屬於比較熱的振動態，振動溫度為893±31 K。對於光解乙二醯二溴分子觀測到的溴分子離去通道，與已知量子產率的化合物比較，決定出其對應的量子產率值為0.06±0.03。

Cavity Ring-Down Spectroscopy (CRDS) has been widely applied in the studies of spectroscopy, kinetics, dynamics, and photochemistry in the condensed or gas phases. The method is based on the measurement of the decay rate of a pulse light trapped in an optical cavity which is formed by a pair of highly reflective(R>99.9%) mirrors. By using cavity ring-down spectroscopy technique, we have observed the channel leading to Br2 molecular elimination following photodissociation of oxalyl bromide at 248 nm. Power dependence measurements are examined, supporting that Br2 molecule were created by the following photodissociation of C2O2Br2, via a single-photon process. The nascent vibrational populations for v” = 0,1, and 2 levels are obtained with a population ratio of 1:(0.65 ± 0.09):(0.34 ± 0.07), corresponding to a Boltzmann-like vibrational temperature of 893 ± 31 K. The quantum yield of the ground state Br2 elimination reaction is determined to be 0.06 ± 0.03.