Vibronic spectrum of pyrazine: New insights from multi-state-multi-mode simulations parameterized with
Paweł Wójcik1, Hanna Reisler1, John F Stanton2
1Department of Chemistry, University of Southern California, Los Angeles, California 90089, USA.
Abstract:
This study reports simulations of the lowest band in the electronic absorption spectrum of pyrazine carried out using a multi-state-multimode vibronic Hamiltonian parameterized using equation-of-motion coupled-cluster methods. The simulations explain the main spectral features and show how peaks of vibronic nature appear. The most complete vibronic model includes four electronic states and six vibrational modes. The simulations reveal that non-adiabatic coupling with bright states located as high as 3 eV above the studied state can lead to discernible features in the absorption spectrum. This study demonstrates the power of fully ab initio treatments of electronic and vibrational structure and their utility in understanding the mechanisms leading to complex molecular spectra.
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