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-C6H4F2…NH3(ND3)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S1和基态S0的键能信息。Ab initio 计算表明,p-C6H4F2…NH3(ND3) 复合物的几何结构是:NH3分子中的N原子位于垂直于p-C6H4F2分子环面的对称轴(Z轴)上,距环面的高度为0.352～nm; NH3的C3轴与p-C6H4F2的对称轴夹角是52.5°,且一个氢原子朝向环面;NH3可绕p-C6H4F2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 der Waals complexes p-C6H4F2…NH3(ND3) through the S1←S0 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-C6H4F2…NH3 in the S1 and S0 states. Ab initio calculation for p-C6H4F2…NH3 gives the following geometry: the N atom of NH3 is located on the symmetry axis (Z-axis) and 0.353～nm above the benzene ring; the C3 axis of NH3 is at an angle of 52.5° with the Z-axis of p-C6H4F2 with one of the hydrogen atoms pointing towards the benzene ring; the rotation of NH3 around the Z-axis is nearly free. The calculataed bond dissociation energy and the prediction of internal rotation are consistent with our experimental results.
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