Ajay J, Šmydke J, Remacle F, Levine R D
The Fritz Haber Center for Molecular Dynamics and Institute of Chemistry, The Hebrew University of Jerusalem , Jerusalem 91904, Israel.
Department of Radiation and Chemical Physics, Institute of Physics, Academy of Sciences of the Czech Republic , 18221 Praha 8, Czech Republic.
J Phys Chem A. 2016 May 19;120(19):3335-42. doi: 10.1021/acs.jpca.6b00165. Epub 2016 Mar 3.
An ultrafast electronic excitation of N2 in the vacuum ultraviolet creates a nonstationary coherent linear superposition of interacting valence and Rydberg states resulting in a net oscillating dipole moment. There is therefore a linear response to an electrical field that can be queried by varying the time delay between the pump and a second optical probe pulse. Both the pump and probe pulses are included in our computation as part of the Hamiltonian, and the time-dependent wave function for both electronic and nuclear dynamics is computed using a grid representation for the internuclear coordinate. Even on an ultrafast time scale there are several processes that can be discerned beyond the expected coherence oscillations. In particular, the coupling between the excited valence and Rydberg states of the same symmetry is very evident and can be directly probed by varying the delay between pulse and probe. For quite a number of vibrations the nuclear motion does not dephase the electronic disequilibrium. However, the nuclear motion does modulate the dipolar response by taking the wave packet in and out of the Franck-Condon region and by its strong influence on the coupling of the Rydberg and valence states. A distinct isotope effect arises from the dependence of the interstate coupling on the nuclear mass.
在真空紫外区域对N₂进行的超快电子激发会产生相互作用的价态和里德堡态的非定常相干线性叠加，从而导致净振荡偶极矩。因此，对电场存在线性响应，可通过改变泵浦脉冲与第二个光学探测脉冲之间的时间延迟来进行探测。泵浦脉冲和探测脉冲在我们的计算中都作为哈密顿量的一部分被包含在内，并且使用核间坐标的网格表示来计算电子和核动力学的含时波函数。即使在超快时间尺度上，也有几个过程超出了预期的相干振荡而可以被辨别出来。特别是，相同对称性的激发价态和里德堡态之间的耦合非常明显，并且可以通过改变脉冲与探测之间的延迟来直接探测。对于相当多的振动，核运动不会使电子非平衡态去相位。然而，核运动确实会通过将波包带入和带出弗兰克 - 康登区域以及对里德堡态和价态的耦合产生强烈影响来调制偶极响应。由于态间耦合对核质量的依赖性，会出现明显的同位素效应。
