用HAM/3法研究胞嘧啶及其甲基衍生物的光电子能谱与紫外光谱

本文用半经验SCF-MO-HAM/3方法计算了胞嘧啶和它的某些甲基衍生物的电离能、激发能和振子强度.指认了这些分子的紫外光电子能谱和紫外电子光谱.讨论了在紫外光电子能谱指认上与CNDO/S的不同之处.分析了胞嘧啶在磷酸三甲酯中可能存在的主要异构体形式.

Photoelectronic spectra and uv spectra of cytosine and its methyl derivatives studied by HAM/3 method

In the present investigation, the vertical ionization energies, excitation energies and oscillator strengths of cytosine and its methyl derivatives were calculated by using a semi-empircal SCF-MO-HAM/3 method proposed by Asbirink et al. Fig. 1 in the Chinese Text is a schematic diagram of some occupied frontier orbitals of cytosine and its methyl derivatives. Fig. 2-4 are correlation diagrams of the experimental and calculated vertical ionization energies of cytosine and its eight methyl derivatives. Fig. 5-7 give HAM/3 assignments of photoelectronic spectra of cytosine and its eight methyl derivatives respectively. Fig. 8-9 show the comparison of UV spectra of cytosine and 3-methyl cytosine with \l\'s calculated by HAM/3. From these figures, it may be seen that the agreement between experimental values and HAM/3 calculations is much better than the results of CNDO/S calculations. The reasons why we prefer the assignments of the first two bands of the UV photoelectron spectra of cytosine and its methyl derivatives by the HAM/3 method to those by the CNDO/S method were fully discussed. The excitation energies and oscillator strengths of four cytosine tautomers were calculated by the HAM/3 configuration- interaction method. The results were compared with UV absorption spectra as shown in Table 1.