1] Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA [2] [3].
Nat Chem. 2013 Nov;5(11):935-40. doi: 10.1038/nchem.1757. Epub 2013 Sep 22.
The ability of liquid water to dissipate energy efficiently through ultrafast vibrational relaxation plays a key role in the stabilization of reactive intermediates and the outcome of aqueous chemical reactions. The vibrational couplings that govern energy relaxation in H2O remain difficult to characterize because of the limitations of current methods to visualize inter- and intramolecular motions simultaneously. Using a new sub-70 fs broadband mid-infrared source, we performed two-dimensional infrared, transient absorption and polarization anisotropy spectroscopy of H2O by exciting the OH stretching transition and characterizing the response from 1,350 cm(-1) to 4,000 cm(-1). These spectra reveal vibrational transitions at all frequencies simultaneous to the excitation, including pronounced cross-peaks to the bend vibration and a continuum of induced absorptions to combination bands that are not present in linear spectra. These observations provide evidence for strong mixing of inter- and intramolecular vibrations in liquid H2O, and illustrate the shortcomings of traditional relaxation models.
液态水通过超快振动弛豫有效地耗散能量的能力在稳定反应中间体和水相化学反应的结果中起着关键作用。由于目前的方法难以同时可视化分子间和分子内运动，因此仍然难以描述控制 H2O 中能量弛豫的振动耦合。使用新的亚 70fs 宽带中红外源，我们通过激发 OH 伸缩跃迁并从 1350cm(-1)到 4000cm(-1)来对 H2O 进行二维红外、瞬态吸收和偏振各向异性光谱研究。这些光谱显示了所有频率的振动跃迁，同时伴随着激发，包括向弯曲振动的明显交峰以及线性光谱中不存在的组合带的连续感应吸收。这些观察结果为液态 H2O 中分子间和分子内振动的强烈混合提供了证据，并说明了传统弛豫模型的局限性。
