Water pentamer: Characterization of the torsional-puckering manifold by terahertz VRT spectroscopy
Water pentamer: Characterization of the torsional-puckering manifold by terahertz VRT spectroscopy
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DOI：
10.1021/jp051504s
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发表时间：
2005-07-28
影响因子：
2.9
通讯作者：
Saykally, RJ
中科院分区：
文献类型：
--
作者：
Harker, HA;Viant, MR;Saykally, RJ
我们提出了通过振动-旋转-隧道（VRT）光谱测量和分析五个新的（D2O）(5)波段，并初步描述了第二个（H2O）(5)波段。所有五个拟合带的振动平均旋转常数与先前观察到的两个（D2O）(5)带的振动平均旋转常数一致，并证实了五聚体在我们实验的时间尺度上平均为对称的准平面结构。而位于50.7 cm(-1) （1.52 THz）和27.3 cm(-1) （0.82 THz）的前两个波段的频谱表明未受扰动的平转子，其余三个（D2O）(5)波段的中心为47.7 cm(-1) (1.43 THz), 45.4 cm(-1) （1.36 THz）和45.0 cm(-1) (1.35 THz)，受到一阶科氏耦合的严重扰动。这代表了第一次观察到这种微扰在渗透水五聚体中，以及第一次观察到扭转-皱缩流形的简并态之间的转变。与Brown等人在89.0 cm（-1）和103.8 cm（-1）波段观察到的（H2O）(5)波段的跃迁不同，5个（D2O）(5)波段的任何一个单独的旋转振动跃迁都没有表现出由于分岔隧道而导致的光谱分裂。通过对这些水五聚体带的仔细分析，我们得出结论，至少有三个扭转折叠流形已经被探测到，并且最低能量的流形是高度紧致的。提出了一种似是而非的水五聚体扭转起皱相关图，尽管需要额外的实验数据来明确地建立扭转起皱能级的能量。
We present the measurement and analysis of five new (D2O)(5) bands via vibration-rotation-tunneling (VRT) spectroscopy as well as a preliminary description of a second (H2O)(5) band. The vibrationally averaged rotational constants of all five fitted bands agree well with those from the two previously observed (D2O)(5) bands and confirm that the pentamer averages to a symmetric, quasi-planar structure on the time scale of our experiment. While the spectrum of the first two bands, located at 50.7 cm(-1) (1.52 THz) and 27.3 cm(-1) (0.82 THz) are indicative of unperturbed oblate rotors, the three remaining (D2O)(5) bands centered at 47.7 cm(-1) (1.43 THz), 45.4 cm(-1) (1.36 THz), and 45.0 cm(-1) (1.35 THz) are severely perturbed by first-order Coriolis coupling. This represents the first observation of this perturbation in the perdeuterated water pentamer, as well as the first observation of transitions between degenerate states of the torsional-puckering manifold. Unlike transitions from the (H2O)(5) band observed by Brown et al. at 89.0 cm(-1) and the 103.8 cm(-1) band that we report here, none of the individual rovibrational transitions of any of the five (D2O)(5) bands demonstrate spectral splittings due to bifurcation tunneling. We conclude, through careful analysis of these water pentamer bands, that at least three torsional-puckering manifolds have been probed and that the lowest-energy manifold is highly compacted. A plausible water pentamer torsional-puckering correlation diagram is proposed, though additional experimental data are required to unambiguously establish the energies of the torsional-puckering levels.