Institut de Química Computacional, Department de Química, Universitat de Girona, Campus de Montilivi, 17071 Girona, Spain.
J Chem Phys. 2011 Oct 7;135(13):134303. doi: 10.1063/1.3643767.
The double bond photoisomerization of fulvene has been studied with quantum dynamics calculations using the multi-configuration time-dependent Hartree method. Fulvene is a test case to develop optical control strategies based on the knowledge of the excited state decay mechanism. The decay takes place on a time scale of several hundred femtoseconds, and the potential energy surface is centered around a conical intersection seam between the ground and excited state. The competition between unreactive decay and photoisomerization depends on the region of the seam accessed during the decay. The dynamics are carried out on a four-dimensional model surface, parametrized from complete active space self-consistent field calculations, that captures the main features of the seam (energy and locus of the seam and associated branching space vectors). Wave packet propagations initiated by single laser pulses of 5-25 fs duration and 1.85-4 eV excitation energy show the principal characteristics of the first 150 fs of the photodynamics. Initially, the excitation energy is transferred to a bond stretching mode that leads the wave packet to the seam, inducing the regeneration of the reactant. The photoisomerization starts after the vibrational energy has flowed from the bond stretching to the torsional mode. In our propagations, intramolecular energy redistribution (IVR) is accelerated for higher excess energies along the bond stretch mode. Thus, the competition between unreactive decay and isomerization depends on the rate of IVR between the bond stretch and torsion coordinates, which in turn depends on the excitation energy. These results set the ground for the development of future optical control strategies.
富烯的双键光致异构化已通过使用多组态含时哈特ree 方法的量子动力学计算进行了研究。富烯是一个测试案例，旨在基于对激发态衰减机制的了解来开发光控策略。衰减发生在几百飞秒的时间尺度内，势能面集中在基态和激发态之间的一个锥形交叉 seam 上。无反应衰减和光致异构化之间的竞争取决于衰减过程中所涉及的 seam 区域。动力学是在一个四维度的模型表面上进行的，该表面由完全活性空间自洽场计算参数化，它捕捉了 seam 的主要特征（能量和 seam 的位置以及相关的分支空间向量）。由持续时间为 5-25 fs、激发能量为 1.85-4 eV 的单个激光脉冲引发的波包传播展示了光动力学前 150 fs 的主要特征。最初，激发能量被转移到键拉伸模式，这导致波包到达 seam，从而促使反应物再生。在振动能从键拉伸转移到扭转模式之后，光致异构化开始。在我们的传播中，沿着键拉伸模式，较高的过剩能量会加速分子内能量重新分配（IVR）。因此，无反应衰减和异构化之间的竞争取决于键拉伸和扭转坐标之间的 IVR 速率，而 IVR 速率又取决于激发能量。这些结果为未来光控策略的发展奠定了基础。
