甲酸及其顺反异构化过渡态的力场、振动频率和异构化反应途径的量子化学研究

QUANTUM CHEMICAL STUDIES ON FORCE FIELDS AND VIBRATIONAL FREQUENCIES OF FORMIC ACID MONOMtR AND TRANSITION STATE AND REACTION ERGODOGRAPHY FOR ITS ISOMERIZATION

用SCF MO ab initio计算,基于3—21G基组,用能量梯度法优化了顺式和反式甲酸分子的平衡几何构型。用反应途径法(reaction pathway)得到了甲酸顺反异构化的过渡态。将模型势函法和MNDO方法结合起来,得到了顺、反甲酸分子的完整力场。利用对角力常数校正因子的可迁性,获得了过渡态的力场,进而求得了各体系的简正振动频率和相应的振动模式。根据RRKM单分子反应理论,得到了相应的频率因子和活化熵值。计算结果与实验观测值进行比较,对分子的性质进行了讨论。

Based on RHF/3-21G basis set, the SCF MO ab initio calculation has been performed on the optimization of the molecular geometries of the cis and trans isomers using the energy gradient method. Transition state for the isomerization is studied by using reaction pathway method. The complete force fields of the cis and trans isomers are determined by the method of determining force field combining model potential function method with MNDO method. Utilizing the transferability of scaled factors for diagonal force constants, the force field of transition state is obtained. Still further, normal vibrational frequencies and modes are ac-quried by means of Wilson-GF matrix method. We also estimate the activated entropy and the reaction frequency factor by using RRKM theory. By comparing the calculated results with observed results, We discuss the properties of Formic acid monomer.