利用步進式掃描時域解析傅氏轉換紅外光譜法研究CH3OSO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光譜儀搭配多重吸收槽，偵測CH3OS(O)Cl/N2或CH3OS(O)Cl/CO2氣體混合樣品經248 nm雷射光解產生CH3OSO於2991、2956、1152及994 cm-1之瞬態吸收譜帶。其中1152 cm-1之譜帶可指派為syn-CH3OSO的S=O振動與CH2左右擺動混合模(ν8，1154 ± 3 cm-1)與S=O振動與CH2上下擺動混合模(ν9，1151 ± 3 cm-1)的貢獻，而994 cm-1之譜帶則可指派為C-O伸張振動模(ν10，994 ± 6 cm-1)的貢獻。而在2991及2956 cm-1之強度較弱的譜帶則可指派為syn-CH3OSO的CH3反對稱伸張振動模(ν2，2991 ± 6 cm-1)與CH3對稱伸張振動模(ν3，2956 ± 3 cm-1)的貢獻。根據理論計算B3P86/aug-cc-pVTZ預測之振動基態與激發態轉動常數與偶極矩導數，吾人利用光譜模擬程式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。此外，anti-CH3OSO之S=O伸張振動模(ν7，1164 cm-1)可能對1152 cm-1之譜帶有少許貢獻。根據吾人假設之動力學模型，可得到CH3OSO自體反應之二級反應常數k5 = (4 ± 2) × 10-10 cm3 molecule-1 s-1。

A step-scan Fourier-transform spectrometer coupled with a multipass absorption cell was employed to detect temporally resolved infrared absorption spectra of CH3OSO produced upon irradiation of a flowing gaseous mixture of CH3OS(O)Cl in N2 or CO2 at 248 nm. Two intense transient features with origins near 1152 and 994 cm-1 are assigned to syn-CH3OSO; the former is attributed to overlapping bands at 1154 ± 3 and 1151 ± 3 cm-1, assigned to the S=O stretching mixed with CH2 rocking (ν8) and the S=O stretching mixed with CH2 wagging (ν9) modes, respectively, and the latter to the C□O stretching (ν10) mode at 994 ± 6 cm-1. Two weak bands at 2991 ± 6 and 2956 ± 3 cm-1 are assigned as the CH3 antisymmetric stretching (ν2) and symmetric stretching (ν3) modes, respectively. Observed vibrational transition wavenumbers agree satisfactorily with those predicted with quantum-chemical calculations at level B3P86/aug-cc-pVTZ. Based on rotational parameters predicted at that level, the simulated rotational contours of these bands agree satisfactorily with experimental results. The simulation indicates that the S=O stretching mode of anti-CH3OSO near 1164 cm-1 likely makes a small contribution to the observed band near 1152 cm-1. A simple kinetic model of self-reaction is employed to account for the decay of CH3OSO and yields a second order rate coefficient k = (4 ± 2)×10-10 cm3 molecule-1 s-1.