摘要
采用含时量子波包理论的简单模型对5-氯尿嘧啶和尿嘧啶的共振拉曼光谱开展了强度分析拟合,获得了1(π,π*)激发态的几何结构变化动态特征.结果表明,尿嘧啶1S0→1S2跃迁的动态结构特征因5-位氯原子取代而改变.5-氯尿嘧啶的动态结构特征主要沿C5襒C6伸缩振动+C6H12弯曲振动和N3H9/N1H7弯曲振动+N1C6伸缩振动反应坐标展开,而尿嘧啶的动态结构特征主要沿嘧啶环的伸缩振动+C5H11/C6H12/N1H7弯曲振动和C4襒O10伸缩振动反应坐标展开.π和π*轨道中氯原子的pz电子参与嘧啶环的p-π共轭作用导致了在1(π,π*)激发态上5-氯尿嘧啶的振动重组能更多地配分给嘧啶环的弯曲振动模式和C5襒C6伸缩振动模式.尿嘧啶在甲醇中的激发态动态结构特征与在水中的基本一致,但波包沿C5H11/C6H12/N1H7弯曲振动+N1C6伸缩振动(ν12)和环呼吸振动(ν17)反应坐标的运动明显增强.
We obtained resonance Raman spectra and UV absorption spectra of 5-chlorouracil and uracil in methanol and in water. B3LYP/6-311＋G（d,p）, B3LYP-TD/6-311＋G（d,p）, and CIS/6-311＋G（d,p） computations were carded out to predict their ground state geometries, ground state vibrational frequencies, electronic transition energies, and 1S2 excited state geometries for 5-chlorouracil and uracil. The resonance Raman spectra of 5-chlorouracil and uracil were assigned based on our FT-Raman and FT-IR measurements and density functional theory calculations. Their absorption cross-sections and absolute resonance Raman cross-sections were quantitatively simulated using the timedependent wave packet formalism. Excited state structural dynamics associated with the lowest singlet ^1（π,π＊） state was obtained. Results indicate that the major feature of the initial excited state structural dynamics of 5-chlorouracil is along the C5=C6 stretch ＋ C6H12 bending and N3H9/N1H7 bending ＋ N1C6 stretch reaction coordinates, while that of uracil is mostly along the ring stretch ＋ ＋C5H11/C6H12/N1H7 bending and C4=O10 stretch reaction coordinates. We conclude that substitution of 5-H by a Cl atom results in a p-π conjugation interaction between the p2 orbital of the Cl atom and the π or π＊ orbital of the pyrimidine ring. This makes the vibrational reorganizational energies more partitioned into the ring bending vibrational modes and the C5=C6 vibrational mode for 5-chlorouracil. The major feature of the initial excited state structural dynamics of uracil in methanol is similar to that in water and the wave-packet motions along the C5H11/ C6H12/N1H7 bending ＋ N1C6 stretch （v12） and the ring breathing （v17） reaction coordinates of uracil are obviously enhanced in methanol relative to those in water.
出处
《物理化学学报》
SCIE
CAS
CSCD
北大核心
2009年第9期1799-1805,共7页
Acta Physico-Chimica Sinica
基金
国家重点基础研究发展计划(973)(2007CB815203)
国家自然科学基金(20573097)
浙江省自然科学基金(R405465)资助项目~~
