Hernández Federico J, Bonafé Franco P, Aradi Bálint, Frauenheim Thomas, Sánchez Cristián G
Universidad Nacional de Córdoba. Facultad de Ciencias Quı́micas , Departamento de Quı́mica Teórica y Computacional , Córdoba Argentina.
Instituto de Investigaciones en Fisicoquímica de Córdoba , INFIQC (CONICET-Universidad Nacional de Córdoba) , Córdoba 5000 , Argentina.
J Phys Chem A. 2019 Mar 14;123(10):2065-2072. doi: 10.1021/acs.jpca.9b00307. Epub 2019 Feb 28.
In the present work we applied a fully atomistic electron-nuclear real-time propagation protocol to compute the impulsive vibrational spectroscopy of the five DNA/RNA nucleobases in order to study the very first steps (subpicosecond) of their energy distribution after UV excitation. We observed that after the pump pulse absorption the system is prepared in a coherent superposition of the ground and the pumped electronic excited states in the equilibrium geometry of the ground state. Furthermore, for relatively low fluency values of the pump pulse, the dominant contribution to the electronic wave function of the coherent state is of the ground state and the mean potential energy surface within the Ehrenfest approximation is similar to that of the ground state. As a consequence, the molecular displacements are better correlated with ground-state normal modes. On the other hand, when the pump fluency is increased the excited-state contribution to the electronic wave function becomes more important and the mean potential energy surface resembles more that of the excited state, producing a better correlation between the molecular displacements and the excited-state normal modes. Finally, it has been observed that the impulsive activation of several vibrational modes upon electronic excitation is triggered by the development of excited-state forces which accelerate the nuclei from their equilibrium positions causing a distribution of the absorbed electronic energy on the nuclear degrees of freedom and could be closely related to the driving force of the ultrafast nonradiative deactivation observed in these systems.
在本工作中，我们应用了一种全原子电子 - 核实时传播协议来计算五种DNA/RNA核碱基的脉冲振动光谱，以便研究它们在紫外激发后能量分布的最初步骤（亚皮秒级）。我们观察到，在吸收泵浦脉冲后，系统在基态平衡几何结构中以基态和泵浦电子激发态的相干叠加态制备。此外，对于泵浦脉冲相对较低的通量值，相干态电子波函数的主要贡献来自基态，并且在埃伦费斯特近似下的平均势能面与基态相似。因此，分子位移与基态简正模式的相关性更好。另一方面，当泵浦通量增加时，激发态对电子波函数的贡献变得更加重要，平均势能面更类似于激发态，使得分子位移与激发态简正模式之间产生更好的相关性。最后，已经观察到电子激发时几种振动模式的脉冲激活是由激发态势能的发展触发的，激发态势能使原子核从其平衡位置加速，导致吸收的电子能量在核自由度上分布，并且可能与在这些系统中观察到的超快非辐射失活的驱动力密切相关。
