Time-resolved vibrational spectroscopies, such as infrared (IR) and Raman spectroscopies, have become increasingly important in modern chemical, biological, and materials research. This modern focus is primarily due to their unique capability to investigate non-equilibrium structural dynamics of ultrafast chemical phenomena. In this work, a computational approach based on both ab-initio molecular dynamics and transient Hessian based vibrational analysis is presented to establish a time-dependent density functional theory (TDDFT) based protocol able of describing simultaneously transient IR and Raman active vibrational modes. This work relies on the recent method development for the evaluation of higher-order TDDFT properties, such as the analytic TDDFT Hessians for excited states. Excited state photo dynamics of prototypical molecules will be used as test cases, showing the evolution of the vibrational “signatures” upon the excitation. This protocol is critical to understand how nuclear motions can mediate the photo-dynamics of several photo-active systems. By observing changes in the vibrational structure and intensity, the developed method can provide a detailed description, at the molecular level, of the ultra-fast photo-induced reactions, showing the power of measuring transient vibrational structures for enabling technological applications, since the study of non-radiative pathways for the energy flow upon excitation is the key to understand and improve the system performances.

New computational methods for excited state time-resolved infrared and Raman scattering spectroscopies

254th National Meeting (2017)

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