复合物p-C_6H_4F_2…NH_3(ND_3)外部振动的共振双光子电离光谱

Resonant Two-photon Ionization Spectra of the Intermolecular Vibrations in p-C_6H_4F_2…NH_3 Complex

利用共振光电离技术和飞行时间质谱技术，观察到了复合物 ｐ－Ｃ_６Ｈ_４Ｆ_２…ＮＨ_３（ＮＤ_３） 的共振双光子电离光谱．光谱分析表明。复合物分子间的伸缩振动频率为 ８６．４ ｃｍ^（－１）；由复合物的 光解离机理以及伸缩模的失谐参数与键能的关系，获得了复合物电子激发态 Ｓ_１和基态 Ｓ_０的键能 信息．Ａｂ ｉｎｉｔｉｏ 计算表明，ｐ－Ｃ_６Ｈ_４Ｆ_５…ＮＨ_３（ＮＤ_３）复合物的几何结构是：ＮＨ_３分子中的 Ｎ 原子位于垂直于ｐ－Ｃ_６Ｈ_４Ｆ_２分子环面的对称轴（Ｚ轴）上，距环面的高度为 ０．３５２ｎｍ； ＮＨ_３的 Ｃ_３轴与ｐ－Ｃ_６Ｈ_４Ｆ_２的对称轴夹角是 ５２．５°；且一个氢原子朝向环面； ＮＨ_３可绕 Ｐ－Ｃ_６Ｈ_４Ｆ_２分子 的Ｚ轴近似的自由转动．键能计算值和预计存在的内转动与实验吻合．

We have studied the resonant two-photon ionizaition (R2PI) spectra of van her Waals complexes p-C_6H_4F_2…NH_3(ND_3) through the S1 ← So transition with mass selectivity. Spectal analysis shows that the stretching frequencies of the complexes is about 86 cm-1. From the photodissociation energy, we estimated the bond energy of the complex p-C_6H_4F_2…NH_3 in the S_1 and S_o states. Ah initio calculation for p-C_6H_4F_2…NH3 gives the following geometry: the N atom of NH_3 is located oil the symmetry axis (Z-axis) and 0.353 urn above the benzene ring; the C_3 axis of NH_3 is at an angle of 52.5° with the Z-axis of p-C_6H_4F_2, with one of the hydrogen atoms pointing towards the benzene ring; the rotation of NH_3 around the Z-axis is nearly free. The calculataed bond dissociation energy and the prediction of internal rotation arc consistent with our experimental results.