Vibrational Dynamics of the Intramolecular H-Bond in Acetylacetone Investigated with Transient and 2D IR Spectroscopy
Vibrational Dynamics of the Intramolecular H-Bond in Acetylacetone Investigated with Transient and 2D IR Spectroscopy
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DOI：
10.1021/acs.jpcb.2c00793
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发表时间：
2022-05-19
影响因子：
3.3
通讯作者：
Fournier, Joseph A.
中科院分区：
文献类型：
--
作者：
Dean, Jessika L. S.;Fournier, Joseph A.
乙酰丙酮（AcAc）已被证明是一个富有成效的，但极具挑战性的模型系统的实验和计算强分子内氢键的审讯。关键问题仍然存在，但是，关于身份的最低能量结构的AcAc和分子内质子转移的动力学。本文利用瞬态吸收光谱和二维红外光谱研究了AcAc及其氘代同位素的烯醇互变异构体的OH/OD伸缩和弯曲区域。OH弯曲区域揭示了在1625 cm-1附近的单一主导对角线过渡，具有到较低频率模式的强烈交叉峰，展示了包含OH弯曲特征的高度混合的指纹过渡。OH弯曲的非谐耦合导致高度伸长的OH弯曲激发态吸收跃迁，这表明OH弯曲泛音/组合带在OH拉伸区域中的大的歧管，导致强的弯曲-拉伸费米共振相互作用。OH和OD拉伸区域包括广泛的基态漂白信号，但没有明确的证据表明，由于强烈的分子内耦合到弯曲，指纹，和低频H-键模式产生的快速人口弛豫，ω 21激发态的漂白。取向弛豫动力学持续的时间尺度长于振动寿命，与极化各向异性组件衰减约2和10个周期内的O-O振荡的OH和OD拉伸，分别。的取向动力学的显着同位素依赖的背景下，分子内模式耦合，扩散过程，质子/氘转移动力学的贡献进行了讨论。
Acetylacetone (AcAc) has proven to be a fruitful but highly challenging model system for the experimental and computational interrogation of strong intramolecular hydrogen bonds. Key questions remain, however, regarding the identity of the minimum-energy structure of AcAc and the dynamics of intramolecular proton transfer. Here, we investigate the OH/OD stretch and bend regions of the enol tautomer of AcAc and its deuterated isotopologue with transient absorption and 2D IR spectroscopy. The OH bend region reveals a single dominant diagonal transition near 1625 cm-1 with intense cross peaks to lower-frequency modes, demonstrating highly mixed fingerprint transitions that contain OH bend character. The anharmonic coupling of the OH bend results in a highly elongated OH bend excited-state absorption transition that indicates a large manifold of OH bend overtone/ combination bands in the OH stretch region that leads to strong bend-stretch Fermi resonance interactions. The OH and OD stretch regions consist of broad ground-state bleach signals, but there is no clear evidence of omega 21 excited-state absorptions due to rapid population relaxation arising from strong intramolecular coupling to bending, fingerprint, and low-frequency H-bond modes. Orientational relaxation dynamics persist for timescales longer than the vibrational lifetimes, with polarization anisotropy components decaying within approximately 2 and 10 periods of the O-O oscillation for the OH and OD stretch, respectively. The significant isotopic dependence of the orientational dynamics is discussed in the context of intramolecular mode coupling, diffusional processes, and contributions from proton/deuteron transfer dynamics.