利用步進式掃描時域解析傅氏轉換紅外光譜法研究C6H5CO之紅外吸收光譜

Abstract

利用步進式掃描時間解析傅氏轉換紅外吸收光譜儀搭配多重吸收槽，以248 nm雷射照射C6H5C(O)CH3/N2或C6H5Br/CO/N2流動混合氣體，成功觀測到C6H5CO於1838、1131、1438及1590 cm-1之瞬態吸收譜帶，可分別指派為C6H5CO之C=O伸張振動模(ν6)，C-C伸張振動與C-H形變振動混合模(ν15)，C1C2C3/C5C6C1對稱伸張振動模(ν10) 與C1C2C3/C4C5C6非對稱伸張振動模(ν7)。此結果與C6H5CO在Ar間質之光譜以及利用B3LYP/aug-cc-pVDZ預測所得之振動波數與紅外吸收相對強度一致。根據理論計算B3LYP/aug-cc-pVDZ預測C6H5CO之振動基態與激發態轉動常數與偶極矩導數，並利用光譜模擬程式SpecView模擬各個振動模的振轉動譜帶，其輪廓與實驗光譜相當吻合。在C6H5Br/CO/N2反應系統中，於反應後期所觀測到的1793、1176及1195 cm-1附近之吸收譜帶與強度較微弱之1687及1277 cm-1附近吸收譜帶分別為C6H5CO後續再與Br及C6H5反應生成之C6H5C(O)Br與C6H5C(O)C6H5所造成的吸收。而於此系統中在反應起始時間所觀測到1902 cm-1附近的微弱吸收，極可能為BrCO之C=O伸張振動模造成的吸收，但需後續研究進行驗證。根據吾人假設之動力學模型，並配合動力學模擬軟體CHEMKIN-II，可得到在363 K與高壓極限條件下，C6H5與CO反應之反應常數k4 = (4.6*10^-14) cm3 molecule-1 s-1以及C6H5CO與Br之反應常數k6 = (1.6*10^-10) cm3 molecule-1 s-1。

A step-scan Fourier-transform infrared spectrometer coupled with a multipass absorption cell was utilized to monitor the gaseous transient species benzoyl radical, C6H5CO. C6H5CO was produced either from photolysis of acetophenone, C6H5C(O)CH3, at 248 nm or in reactions of phenyl radical (C6H5) with CO; C6H5 was produced on photolysis of C6H5Br at 248 nm. One intense band at 1838 cm-1, one weak band at 1131 cm-1, and two extremely weak bands at 1438 and 1590 cm-1 are assigned to the C=O stretching (ν6), the C-C stretching mixed with C-H deformation (ν15), the out-of-phase C1C2C3/C5C6C1 symmetric stretching (ν10), the in-phase C1C2C3/C4C5C6 antisymmetric stretching (ν7) modes of C6H5CO, respectively. These observed vibrational wavenumbers and relative IR intensities agree with those reported for C6H5CO isolated in solid Ar and with values predicted for C6H5CO with the B3LYP/aug-cc-pVDZ method. The rotational contours of the two bands near 1838 and 1131 cm-1 simulated according to rotational parameters predicted with the B3LYP/aug-cc-pVDZ method fit satisfactorily with the experimental results. Additional products BrCO, C6H5C(O)Br and C6H5C(O)C6H5 were identified in the C6H5Br/CO/N2 experiments; the kinetics involving C6H5CO and C6H5C(O)Br are discussed.