Herperger Katherine R, Krumland Jannis, Cocchi Caterina
Department of Physics, University of Ottawa, Ottawa ON K1N 6N5, Canada.
Physics Department and IRIS Adlershof, Humboldt-Universität zu Berlin, 12489 Berlin, Germany.
J Phys Chem A. 2021 Nov 11;125(44):9619-9631. doi: 10.1021/acs.jpca.1c06538. Epub 2021 Oct 29.
Among polycyclic aromatic hydrocarbons, pyrene is widely used as an optical probe thanks to its peculiar ultraviolet absorption and infrared emission features. Interestingly, this molecule is also an abundant component of the interstellar medium, where it is detected via its unique spectral fingerprints. In this work, we present a comprehensive first-principles study on the electronic and vibrational response of pyrene and its cation to ultrafast, coherent pulses in resonance with their optically active excitations in the ultraviolet region. The analysis of molecular symmetries, electronic structure, and linear optical spectra is used to interpret transient absorption spectra and kinetic energy spectral densities computed for the systems excited by ultrashort laser fields. By disentangling the effects of the electronic and vibrational dynamics via simulations with stationary and moving ions, and, in specific cases, with the aid of auxiliary model systems, we rationalize that the nuclear motion is mainly harmonic in the neutral species, while strong anharmonic oscillations emerge in the cation, driven by electronic coherence. Our results provide additional insights into the ultrafast vibronic dynamics of pyrene and related compounds and set the stage for future investigations on more complex carbon-conjugated molecules.
在多环芳烃中，芘因其独特的紫外吸收和红外发射特性而被广泛用作光学探针。有趣的是，这种分子也是星际介质的丰富成分，在那里通过其独特的光谱指纹被检测到。在这项工作中，我们对芘及其阳离子在紫外区域与它们的光学活性激发共振的超快、相干脉冲作用下的电子和振动响应进行了全面的第一性原理研究。通过对分子对称性、电子结构和线性光谱的分析，来解释为超短激光场激发的系统计算的瞬态吸收光谱和动能谱密度。通过使用固定离子和移动离子的模拟，并在特定情况下借助辅助模型系统，来解开电子和振动动力学的影响，我们推断出中性物种中的核运动主要是简谐的，而在阳离子中，由电子相干驱动会出现强烈的非简谐振荡。我们的结果为芘及相关化合物的超快振动电子动力学提供了更多见解，并为未来对更复杂的碳共轭分子的研究奠定了基础。
