外电场对甲醛分子的结构与电子光谱的影响

Influence of external electric field on the molecular structure and electronic spectrum of formaldehyde molecule

采用密度泛函理论(DFT)在B3LYP/6-311++G(d,p)基组水平上,计算了不同外加电场(-8.22×10~9~8.22×10~9 V/m)下甲醛分子基态稳定构型、分子键长、电荷分布、能级分布、能隙、红外光谱、拉曼光谱和分子的总能量.在此基础上利用TDDFT/B3LYP/6-311++G(d,p)方法研究了甲醛分子由基态跃迁到前25个激发态的激发能E、谐振强度f、吸收波长λ受外电场的影响.结果表明:随着C=O连线方向外电场的增加,C=O键键长、氢原子电荷、偶极矩和能隙递增;C—H键键长、C,O原子电荷递减,总能量降低.振动频率与红外强度及拉曼强度由于不同振动有不同变化.甲醛分子UV-Vis光谱随外电场的增加,不同的吸收峰发生了不同程度的蓝移或者红移;外电场对甲醛分子的激发能、谐振强度和吸收波长的强度有一定影响,但随电场变化比较复杂.

The density function theory （DFT） at B3LYP/6-311 ＋＋G（d,p） level was used to calcu- late the molecular stable configuration, bond length, charge distribution, energy distribution, energy gap,infrared spectra, raman spectra and total energies of the ground state of formaldehyde molecule under different external electric fields （-8.22× 109-8.22 × 109 V/m）. Based on this step, the time dependent density functional theory （TDDFT） was used to study the influences of external electric field on the excited energies,wavelengths and oscillators of the first 25 excited states. The results showed that bond lengths of C = O, hydrogen charge, dipole moment and energy gap increased, and bond lengths of C--H, the charge of carbon atom,oxygen charge and total energy decreased with the increase of electric field along C = O direction. Electric fields had effects on excitation energy,oscilla- tor strength and absorption wavelength of the formaldehyde, but changing with the electric field was more complex.