Terahertz laser vibration-rotation tunneling spectroscopy of the water tetramer
Terahertz laser vibration-rotation tunneling spectroscopy of the water tetramer
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DOI：
10.1021/jp970782r
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发表时间：
1997-11-27
影响因子：
2.9
通讯作者：
Saykally, RJ
中科院分区：
文献类型：
--
作者：
Cruzan, JD;Viant, MR;Saykally, RJ
在2.04太赫兹（67.9 cm(-1)）附近记录了（H2O）(4)的振动-旋转-隧穿（VRT）谱。这个δ K = 0对称转子光谱的波段原点被移了0.1 cm(-1)，变成了先前报道的（D2O）(4)波段的蓝色[Science， 1996,271, 59]。与该光谱类似，（H2O）(4)光谱中的每个跃迁都表现出规则的双重态分裂。（D2O）(4)和（H2O）(4)双重态间距分别为5.6和2260 MHz，作为旋转的函数是恒定的，表明存在简并隧穿分裂。在S-4平衡结构中，不参与氢键的H原子的协调翻转运动，类似于氨转化，使它们合理化。在分子对称基团C-4h(M)中，这两个波段都被分配到最低的A(g)- >B-g分子间振动。在D2O和H2O四聚体光谱中都发现了额外的K = 2分裂，且分裂随J的增加呈非线性增加。在水三聚体VRT数据中观察到分岔隧道运动的证据，但在（H2O）(4)光谱中发现了（H2O）(4)的证据，其形式是展宽的谱线，可能包含未解析的分岔隧道分裂。数据的结构估计表明，（D2O）(4)和（H2O）(4)中的氧间分离与该参数的指数收缩一致，作为簇大小增加的函数。
A vibration-rotation-tunneling (VRT) spectrum of (H2O)(4) has been recorded near 2.04 THz (67.9 cm(-1)). The band origin of this Delta K = 0 symmetric rotor spectrum is shifted by 0.1 cm(-1) to the blue of that of a (D2O)(4) band reported previously [Science, 1996, 271, 59]. Similar to that spectrum, each transition in the (H2O)(4) spectrum exhibits a regular doublet splitting. The (D2O)(4) and (H2O)(4) doublet spacings, 5.6 and 2260 MHz, respectively, are constant as a function of rotation, indicative of degenerate tunneling splittings. They have been rationalized in terms of a concerted flipping motion of the H atoms that do not participate in hydrogen bonding in the S-4 equlibrium structure, analogous to ammonia inversion. Both bands have been assigned to the lowest A(g)-->B-g intermolecular vibration in the molecular symmetry group C-4h(M). Additional K = 2 splittings, which increase nonlinearly with increasing J, were found in both D2O and H2O tetramer spectra. Evidence for the bifurcation tunneling motion observed in the water trimer VRT data, but not in evidence for (D2O)(4), was found in the (H2O)(4) spectrum in the form of broadened lines probably containing unresolved bifurcation tunneling splittings. Structural estimates from the data indicate that the interoxygen separations in both (D2O)(4) and (H2O)(4) are consistent with an exponential contraction in that parameter as a function of increasing cluster size.