利用步進式時域解析霍氏轉換紅外光譜法研究丙烯醯氯於193 nm光解產生一氧化碳及氯化氫之內能分佈

Abstract

本實驗利用步進式時域解析霍氏紅外放光光譜法研究丙烯醯氯於193 nm之光解反應，藉由觀測產物CO及HCl的振-轉動放光譜線，分析其內能分佈，並進一步進行反應探討。 丙烯醯氯於193 nm光解後可觀測到光區1865－2300 cm-1之放光譜線中，產物CO分布到v≤4、J’≤46，其平均轉動能量為21.6 ± 7.4 kJ mol-1，平均振動能量為13.0 ± 3.6 kJ mol-1；並可觀察到兩種振動能分佈趨勢，分別為Tvib1 ≈ 16400 K及Tvib2 ≈ 1700 K。兩者之CO比例約為5: 95；而於光區2350－3250 cm-1中觀測產物HCl分布至v≤7、J’≤13之放光譜線，且兩種HCl內能分佈分別是：低轉動、低振動者為途徑A，其平均轉動能量為9.9 ± 2.5 kJ mol-1，平均振動能量為21.2 ± 3.9 kJ mol-1。高轉動、高振動者為途徑 B，其平均轉動能量為36.3 ± 5.3 kJ mol-1，平均振動能量為45.7 ± 2.5 kJ mol-1；兩者HCl比例約為21: 79。 由理論計算位能圖及反應分支比，可以指認途徑-A為s-trans-CH2CHC(O)Cl經1,3-Cl重排後的ClCH2CHCO四中心分解 (反應2-a) 後產生HCl；途徑-B係s-cis-CH2CHC(O)Cl四中心分解 (反應2-b) 後產生HCl。至於產物CO則有四種可能來源，分別為兩不同途徑的C-Cl斷鍵[反應(1-a)、(1-b)] 的產物CH2CHCO及上述兩HCl分解反應(2-a)、(2-b)的產物CH2CCO二次分解而來。根據各個產物的比例及途徑(1)、(2)分支比，指認具高振動能量的CO來自反應途徑(2-a)的CH2CCO二次分解。並且，由各自由基的結構及內能分布結果判斷，s-trans-CH2CHĊO及s-cis-CH2CHĊO較可能為分解產生CO的前驅物。 相較於Su研究組的結果[3]，由於本實驗的光譜訊雜比較佳及分析方法精確，故得以藉由觀測到的產物紅外放光，對丙烯醯氯的光解反應得到較多資訊，尤其是兩種HCl之產生途徑。在能量計量方面，本實驗所得之產物內能結果與Butler研究組[5]的移動能實驗數據相輔相成，能夠合理地推論產物來源及內能分佈情形。

Photodissociation of acryloyl chloride at 193 nm has been investigated with a step-scan time-resolved Fourier-transform emission spectrometer. Two major rotationally resolved bands in regions 1865－2300 cm-1 and 2350－3250 cm-1 are observed; and assigned as emission of CO(v  4, J’  36) and HCl(v  7, J’  13), respectively. An approximate rotational temperature of 2500 ± 640 K can be used to fit the CO emission spectrum, and the average rotational energy is 9.9 ± 2.5 kJ mol-1. However, the vibrational distribution might be consider as bimodal, with two components having vibrational temperature of 16400 K and 1700 K, and average vibrational energies of 95.7 and 5.0 kJ mol-1, respectively. The population ratio of these two CO channels is approximately5: 95. The rotational distribution of HCl is bimodal. The low-J component has a rotational temperature of 1000 ± 70 K and vibrational temperature of 4900 ± 530 K, corresponding to channel A. The high-J component has a rotational temperature of 4800 ± 580 K and vibrational temperature of 8000 ± 450 K, corresponding to channel B. The average rotational energy and vibrational energy of these two channels are 9.9 ± 2.5 kJ mol-1 and 21.2 ± 3.9 kJ mol-1 for channel A and 36.3 ± 5.3 kJ mol-1 and 45.7 ± 2.5 kJ mol-1 for channel B. The population ratio of channel A to channel B is determined to be approximately 21:79. With the aid of calculations and branching ratio of products from various channels, we could contribute channel A of HCl to the decomposition of s-trans-CH2CHC(O)Cl after 1,3-migration, reaction (2-a), and channel B of HCl to the direct decomposition of s-cis-CH2CHC(O)Cl , reaction (2-b). Accordingly, we contribute the high-v component of CO to the secondary dissociation of the product CH2CCO of reaction (2-a) and the low-v component of CO to an average results, which combine the secondary dissociation of product CH2CHCO from reaction (1) with the secondary dissociation of product CH2CCO from reaction (2-b). Our results of internal-state distribution are complementary to Butler’s results [5] on kinetic energy distributions. With these results, we provide a more detailed understanding on the energy distribution and branching of each reaction channel.