Electron configuration changes in excited pyrazine molecules analyzed by femtosecond time-resolved photoelectron spectroscopy

Abstract

Using the pump–probe technique with 130 fs laser pulses near 200 nm and near 266 nm the internal conversion of the pyrazine molecule excited to the S2 state has been studied. The lifetime of the S2 state due to internal conversion to the lower electronic states is τIC(2)=(20±10) fs while the lifetime of the secondarily populated S1 state is τIC(1)=(22±1) ps. The results of femtosecond time-resolved electron spectroscopy directly demonstrate the variation of the electron configuration during the internal conversion: The electron spectrum changes significantly on the fs time scale for pyrazine ions produced by ionization via the S2 state with ππ* character and by ionization of S1 state molecules with nπ* configuration after the internal conversion, respectively. The results obtained confirm theoretical estimations of Domcke and co-workers [J. Chem. Phys. 95, 7806 (1991); J. Phys. Chem. 97, 12466 (1993)] who describe the internal conversion in the pyrazine molecule on the basis of a conical intersection of the corresponding potential energy surfaces.

Dynamics of radiationless transitions in large molecular systems: A Franck–Condon-based method accounting for displacements and rotations of all the normal coordinates

“…49 Theoretical computations have confirmed the existence of a conical intersection between the two excited states, 42 moreover, quantum dynamic computations based on the vibronic coupling mechanism were able to reproduce the shape of the S 0 → S 2 absorption band. 41,[50][51][52] In order to apply the procedure outlined in the previous section to the dynamics of the S 2 → S 1 internal conversion, the equilibrium geometries, the harmonic frequencies and the normal modes of the ground state and of the two crossing excited states are necessary.…”

Femtosecond Time-Resolved Photoelectron Spectroscopy

“…In 2000, Radloff and co-workers applied TRPES to the famous pyrazine S 2 lifetime problem, 137 connecting with Domcke's earlier calculations. Using short UV laser pulses (∼130 fs), Radloff excited pyrazine S 2 with two different wavelengths: 200 (6.2 eV) and 196 nm (6.31 eV).…”

Efficient on-the-fly ab initio semiclassical method for computing time-resolved nonadiabatic electronic spectra with surface hopping or Ehrenfest dynamics

“…(28) by generalizing Eqs. (45) and (46) beyond the Condon approximation. Note that μ W (X) = μ (Q) sinceμ is independent of nuclear momentum.…”

“…The pyrazine molecule exhibits a conical intersection between the first (S 1 ) and second (S 2 ) bright excited states, which influences the dynamics after excitation and the resulting vibronic spectra. Because the pyrazine molecule provides an almost ideal benchmark, its vibronic spectra have been extensively studied both experimentally [37][38][39][40][41][42][43][44][45][46] and theoretically, 6,25,26,31,[47][48][49][50][51][52][53][54][55][56][57][58][59][60][61][62] giving us an opportunity not only to assess the accuracy of the MSDR in relation to experiment but also to compare it with exact quantum calculations on simplified models developed by others. In addition, due to efficiency of the MSDR, we were able to go beyond simplified model systems and to compute the absorption spectrum using the ab initio electronic structure computed on the fly in all 24 dimensions.…”