Hernandez Federico J, Brice Joseph T, Leavitt Christopher M, Liang Tao, Raston Paul L, Pino Gustavo A, Douberly Gary E
Department of Chemistry, University of Georgia, Athens, Georgia 30602, USA.
Department of Chemistry and Biochemistry, James Madison University, Harrisonburg, Virginia 22807, USA.
J Chem Phys. 2015 Oct 28;143(16):164304. doi: 10.1063/1.4933432.
Small water clusters containing a single hydroxyl radical are synthesized in liquid helium droplets. The OH-H2O and OH(D2O)n clusters (n = 1-3) are probed with infrared laser spectroscopy in the vicinity of the hydroxyl radical OH stretch vibration. Experimental band origins are qualitatively consistent with ab initio calculations of the global minimum structures; however, frequency shifts from isolated OH are significantly over-predicted by both B3LYP and MP2 methods. An effective Hamiltonian that accounts for partial quenching of electronic angular momentum is used to analyze Stark spectra of the OH-H2O and OH-D2O binary complexes, revealing a 3.70(5) D permanent electric dipole moment. Computations of the dipole moment are in good agreement with experiment when large-amplitude vibrational averaging is taken into account. Polarization spectroscopy is employed to characterize two vibrational bands assigned to OH(D2O)2, revealing two nearly isoenergetic cyclic isomers that differ in the orientation of the non-hydrogen-bonded deuterium atoms relative to the plane of the three oxygen atoms. The dipole moments for these clusters are determined to be approximately 2.5 and 1.8 D for "up-up" and "up-down" structures, respectively. Hydroxyl stretching bands of larger clusters containing three or more D2O molecules are observed shifted approximately 300 cm(-1) to the red of the isolated OH radical. Pressure dependence studies and ab initio calculations imply the presence of multiple cyclic isomers of OH(D2O)3.
在液氦滴中合成了含有单个羟基自由基的小水团簇。利用红外激光光谱在羟基自由基OH伸缩振动附近对OH-H₂O和OH(D₂O)ₙ团簇（n = 1 - 3）进行了探测。实验带起源与全局最小结构的从头算计算在定性上是一致的；然而，B3LYP和MP2方法都显著高估了与孤立OH相比的频率位移。使用一个考虑电子角动量部分猝灭的有效哈密顿量来分析OH-H₂O和OH-D₂O二元复合物的斯塔克光谱，揭示了一个3.70(5) D的永久电偶极矩。当考虑大振幅振动平均时，偶极矩的计算与实验结果吻合良好。采用偏振光谱对归属于OH(D₂O)₂的两个振动带进行表征，揭示了两个能量几乎相等的环状异构体，它们在非氢键合氘原子相对于三个氧原子平面的取向上有所不同。对于这些团簇，“上-上”和“上-下”结构的偶极矩分别确定为约2.5 D和1.8 D。观察到含有三个或更多D₂O分子的较大团簇的羟基伸缩带向孤立OH自由基的红色区域移动了约300 cm⁻¹。压力依赖性研究和从头算计算表明OH(D₂O)₃存在多种环状异构体。
