Berner G M, East A L L, Afshari Mahin, Dehghany M, Moazzen-Ahmadi N, McKellar A R W
Department of Chemistry and Biochemistry, University of Regina, Regina, Saskatchewan S4S 0A2, Canada.
J Chem Phys. 2009 Apr 28;130(16):164305. doi: 10.1063/1.3121224.
Improved quantum chemistry (coupled-cluster) results are presented for spectroscopic parameters and the potential energy surface for the N(2)O dimer. The calculations produce three isomer structures, of which the two lowest energy forms are those observed experimentally: a nonpolar C(2h)-symmetry planar slipped-antiparallel geometry (with inward-located O atoms) and a higher-energy polar C(s)-symmetry planar slipped-parallel geometry. Harmonic vibrational frequencies and infrared intensities for these isomers are calculated. The low-frequency intermolecular vibrational mode predictions should be useful for future spectroscopic searches, and there is good agreement in the one case where an experimental value is available. The frequency shifts for the high-frequency intramolecular stretching vibrations, relative to the monomer, were calculated and used to help locate a new infrared band of the polar isomer, which corresponds to the weaker out-of-phase combination of the nu(1) antisymmetric stretch of the individual monomers. The new band was observed in the region of the monomer nu(1) fundamental for both ((14)N(2)O)(2) and ((15)N(2)O)(2) using a tunable infrared diode laser to probe a pulsed supersonic jet expansion, and results are presented.
给出了改进的量子化学（耦合簇）计算结果，涉及N₂O二聚体的光谱参数和势能面。计算得到了三种异构体结构，其中能量最低的两种形式是实验中观察到的：一种是非极性的C₂h对称平面滑移反平行几何结构（O原子位于内侧），以及一种能量较高的极性Cs对称平面滑移平行几何结构。计算了这些异构体的谐波振动频率和红外强度。低频分子间振动模式的预测结果对未来的光谱研究应该是有用的，并且在有实验值的一种情况下，两者吻合良好。计算了高频分子内拉伸振动相对于单体的频率位移，并用于帮助定位极性异构体的一个新红外波段，该波段对应于各个单体的ν₁反对称拉伸的较弱异相组合。使用可调谐红外二极管激光器探测脉冲超声速射流膨胀，在(¹⁴N₂O)₂和(¹⁵N₂O)₂的单体ν₁基频区域均观察到了这个新波段，并给出了结果。
