运用密度泛函理论在B3LYP/6-31++G**理论水平研究N,N-二甲基脲二聚体和三聚体氢键结构.构型优化和频率计算得到3个稳定的二聚体和三聚体氢键异构体.经基组重叠误差和零点振动能校正后,最稳定的二聚体和三聚体的相互作用能分别为-48.52和-72.15 kJ/mol.振动分析表明二聚体和三聚体存在典型的红移氢键.热力学分析显示,298.15 K和标准压力下,二聚体和三聚体的形成是一个放热过程.Abstract：The hydrogen bonding structures of the N,N-Dimethylurea dimer and trimer have been investigated using density functional theory at B3LYP/6-31++G** level. Three stable structures of the dimer and trimer have been obtained by the optimized geometries and frequencies calculation. After basis set superposition error and zero-point vibration energy correction, it is found that the most stable dimer and trimer have strong hydrogen bonding interaction with -48.52 and -72.15 kJ/mol. Vibration analysis show that dimer and trimer have typical red-shift hydrogen bond. In addition, thermal stability indicates that the formation of dimer and trimer at 298.15K and standard pressure is a exothermic process.
结合DDS、PLL、倍频及混频技术,研制了一种低相噪和低杂散的毫米波全相参雷达频综.主要包括一个毫米波频率源、一个线性调频信号发生器以及为接收机提供第二本振的微波源,整个源的相参时钟采用外接的一个100 MHz恒温晶振提供.分析和估算了毫米波信号的相位和杂散.测试结果表明信号输出频率范围为34.855 GHz^34.865 GHz,步进100 k Hz,输出功率高于16 d Bm,相位噪声大约为-92 d Bc/Hz@10 k Hz。
