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化学学报
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化学学报 ›› 2013, Vol. 71 ›› Issue (05): 761-768.DOI: 10.6023/A13020166 上一篇    下一篇

研究论文

乙酰乙酸乙酯在重水和环己烷中的C=O和C=C伸缩振动模式的振动衰减动力学

刘英亮, 杨帆, 王建平   

  1. 北京分子科学国家实验室 分子反应动力学实验室 中国科学院化学研究所 北京 100190
  • 投稿日期:2013-02-01 发布日期:2013-03-21
  • 通讯作者: 王建平jwang@iccas.ac.cn;杨帆,fanyang@iccas.ac.cn; Tel: 010-62656806, Fax: 010-62563167 E-mail:jwang@iccas.ac.cn;fanyang@iccas.ac.cn
  • 基金资助:

    项目受中国科学院知识创新工程(No. KJCX2-EW-H01)、“百人计划”和国家自然科学基金(Nos. 20727001, 91121020和21103200)资助.

Ultrafast Vibrational Relaxation Dynamics of C=O and C=C Stretching Modes of Ethyl Acetoacetate in Deuterated Water and Cyclohexane

Liu Yingliang, Yang Fan, Wang Jianping   

  1. Beijing National Laboratory for Molecular Sciences, Molecular Reaction Dynamics Laboratory, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190
  • Received:2013-02-01 Published:2013-03-21
  • Supported by:

    Project supported by the Knowledge Innovation Program (No. KJCX2-EW-H01), the Hundred Talent Fund from the Chinese Academy of Sciences and the National Natural Science Foundation of China (Nos. 20727001, 91121020 and 21103200).

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作为典型的β-二羰基化合物和α,β-烯酮类化合物, 乙酰乙酸乙酯在溶液中以多结构存在. 在本文中, 我们利用飞秒中红外泵浦探测光谱技术, 研究了该化合物在重水和环己烷溶液中不同互变异构体的出现在波长6 μm(频率范围1600～1800 cm-1)区域的C=O和C=C伸缩振动的振动动力学; 并结合稳态红外实验和量子化学计算, 分析了这些吸收峰的线型特征. 结果表明: 在重水中, 乙酰乙酸乙酯以酮式存在; 而在环己烷中以烯醇式和两种酮式共存. 分析稳态红外光谱可以看到, 烯醇式结构刚性, 其红外光谱线型主要表现为均匀增宽; 而酮式的线型则兼具均匀增宽和非均匀增宽. 而且, 即使在同一种溶剂中, 酮式和烯醇式的表观红外光谱线型也有不同. 通过泵浦探测实验获得了C=O和C=C伸缩振动衰减动力学和各向异性动力学. 重水中酮式的C=O的振动能量弛豫过程比其在环己烷中要快, 这可归因于乙酰乙酸乙酯与溶剂发生的分子间氢键作用. 此外, 烯醇式的C=O伸缩振动和一些振动模式(如COH面内弯曲)之间存在费米共振, 直接影响其快速衰减过程, 这也是造成其振动衰减动力学不同于酮式的原因. 各向异性动力学过程表明, 乙酰乙酸乙酯在重水中的转动速度比其在环己烷中要慢一些, 与它们不同的溶剂化情况有关. 此外, 各向异性动力学过程表现出量子拍频现象, 在酮式中尤为明显, 意味着相关振动模式存在相干激发.

关键词: 红外泵浦探测, 振动能量弛豫动力学, 各向异性动力学, 乙酰乙酸乙酯

As a prototype of both β-diketone and α,β-enone compounds, ethyl acetoacetate (EAC) has been known to exist in multiple structures in solutions. In this paper, femtosecond infrared pump-probe spectroscopy was used to examine the vibrational relaxation processes of the C=O and C=C stretching modes, appeared in the region of 6 μm wavelength (1600～1800 cm-1 in frequency), of the EAC tautomers in deuterated water (D2O) and cyclohexane. Steady-state infrared spectroscopy and quantum chemistry computations were used to understand the characteristics of these vibrational bands and their line shapes. The results showed that in water EAC exists in the keto form, while in cyclohexane it exists in both keto and enol forms, and perhaps in two possible keto forms. As a result of structural rigidity, the steady-state infrared absorption peak is narrow for the enol form, suggesting mainly homogenous broadening; while those of the keto form exhibit the feature of both homogenous and heterogeneous broadenings. The apparent infrared line shapes of the keto and enol forms were somewhat different even in the same solvent. Population dynamics and anisotropy dynamics of the C=O and C=C stretching mode were obtained and examined by transient infrared pump-probe measurement. In D2O, the vibrational energy relaxation rate of the C=O modes was found to be faster than that in cyclohexane, which can be attributed to the formation hydrogen bond between EAC and solvent molecules. The vibrational relaxation process of the enol form was found to be different from that of the keto form, which can be contributed to Fermi resonance interaction between the C=O stretching mode and the COH bending mode. With the aid of the quantum chemistry calculations, it is concluded that there exists a fast vibrational population equilibrium process between the C=O and C=C stretching modes and the COH in-plane bending mode via Fermi resonance. Anisotropy experiments showed a fast orientation dynamics for EAC in cyclohexane than in water, reflecting different solvations. Further, quantum beating was observed in the anisotropy dynamics due to the coherence between the ss- and as-modes, especially for the keto form, suggesting a coherent excitation between the related vibrational modes.

Key words: IR pump-probe, vibrational energy relaxation dynamics, anisotropy dynamics, ethyl acetoacetate