Excited state vibronically relaxed

If the system under consideration possesses non-adiabatic electronic couplings within the excited-state vibronic manifold, the latter approach no longer is applicable. Recently, we have developed a simple model which allows for the explicit calculation of RF s for electronically nonadiabatic systems coupled to a heat bath [2]. The model is based on a phenomenological dissipation ansatz which describes the major bath-induced relaxation processes excited-state population decay, optical dephasing, and vibrational relaxation. The model has been applied for the calculation of the time and frequency gated spontaneous emission spectra for model nonadiabatic electron-transfer systems. The predictions of the model have been tested against more accurate calculations performed within the Redfield formalism [2]. It is natural, therefore, to extend this... 

Ionization techniques can lead to the formation of not only the ground electronic state of a molecular ion, but also excited electronic states, both by direct ionization and by autoionization. Such excited states may react directly and they may emit radiation. They may decay to other electronic states (vibronic relaxation) and then undergo reaction. All these processes may be in competition with each other [711]. 

Condensed phase vibrational or vibronic lineshapes (vibronic transitions create vibrational excitations of electronic excited states) rarely provide infonnation about VER (see example C3.5.6.4). Experimental measurements of VER need much more than just the vibrational spectmm. The earliest VER measurements in condensed phases were ultrasonic attenuation studies of liquids [15], which provided an overall relaxation time for slowly (>10 ns) relaxing small molecule liquids. 

The first type of interaction, associated with the overlap of wavefunctions localized at different centers in the initial and final states, determines the electron-transfer rate constant. The other two are crucial for vibronic relaxation of excited electronic states. The rate constant in the first order of the perturbation theory in the unaccounted interaction is described by the statistically averaged Fermi golden-rule formula... 

In the nanosecond biphotonic photolysis the vibronically excited level reached by absorption of the first photon relaxes by IC to the first excited state (Figure 3), which is stronger acid than the ground state by up to six orders in magnitude [11]. Quantum chemical calculations showed that the O - H bond becomes a bit longer and the C - OH bond becomes shorter and more rigid. The lifetimes of the first excited singlet state of the sterically hindered phenols... 

In the case of 5T and 6T, the excited states with B symmetry near 4 eV can be occupied by allowed one-photon excitation from the A ground state. For 3T and 4T, states of A symmetry lie next to the excited state. They need vibronic coupling to be excited. The initially occurring absorption A0 is assumed to start from one of the higher electronic states near 4 eV. Relaxation processes from these states may be responsible for the decay of A0 during the first picosecond and for the delayed increase of stimulated fluorescence of 3T-6T. 

The high-energy excitation, hw, > h(o2 + hS20, is also due to the vibronic components at 390 and 1400 cm- . If we privilege the vibronic relaxation by fission and the creation of one vibration hQ0, then the relaxation of the incident photon h(ot leads to a state about 100 cm-1 above the observed emission. The excitation spectrum due to the vibronic component at 1400 cm-1 (see Fig. 3.18) shows that the relaxation by creation of other vibrations contributes also, since no threshold structure is observed around the value hco2 + 1400 cm-1. This conclusion is also consistent with the vibronic analysis of the bulk (Section II.B.3). 

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