TY - JOUR T1 - Theoretical Treatment of Ultrafast Decay of Excited Vibronic States in the Improved Adiabatic Approximation JO - Communications in Computational Chemistry VL - 4 SP - 110 EP - 120 PY - 2018 DA - 2018/10 SN - 5 DO - http://doi.org/10.4208/cicc.2017.v5.n4.2 UR - https://global-sci.org/intro/article_detail/cicc/12750.html KW - Pyrazine, Born-Oppenheimer approximation, internal conversion, DFT. AB -

In the present paper, the non-radiative transition ${\rm S}_1→{\rm S}_0$ of pyrazine was investigated by employing the improved Born-Oppenheimer adiabatic approximation, in which the conical intersection is shown to be avoided. Vibrational frequencies, normal coordinates, and non-adiabatic coupling matrix elements were obtained by ab initio quantum chemical methods. Calculated rate constants of internal conversion ${\rm S}_1→{\rm S}_0$ are $τ(υ=0)=61.7 $ ps and $τ(υ=1)=61.2$ ps in good agreement with the experimental findings.