Adiabatic excited state

In the excited state, the redistribution of electrons can lead to localized states with distinct fluorescence spectra that are known as intramolecular charge transfer (ICT) states. This process is dynamic and coupled with dielectric relaxations in the environment [16]. This and other solvent-controlled adiabatic excited-state reactions are discussed in [17], As shown in Fig. 1, the locally excited (LE) state is populated initially upon excitation, and the ICT state appears with time in a process coupled with the reorientation of surrounding dipoles. 

Figure 13. Comparison of quantum (thick hues), QCL (thin lines), and SH (dashed lines) results as obtained for the one-mode two-state model IVa [205], Shown are (a) the adiabatic excited-state population P i), (b) the corresponding diabatic population probability and (c) the...

Figure 14. Statistical error of the adiabatic excited-state population at times r = 10 fs ( ), 30 fs -f), and 50 fs (X x x) for Model IVa [205], plotted as a function of the number of iterations N. The full lines represent fits to a 1 / /N dependence.

Twenty configurations from a 35 ps ground state adiabatic trajectory, chosen to be on resonance with the laser bandwidth corresponding to the experiments, were selected as the starting points for non-adiabatic excited state trajectories. A corresponding set of trajectories was run in D2O, with a model identical in all respects to the work described previously except that the mass of the H atom was changed from 1 to 2 amu, and preliminary results of the behavior in D2O are included here. 

B. C. Garrett and D. G. Truhlar, WKB approximation for the reaction-path Hamiltonian Application to variational transition state theory, vibrationally adiabatic excited-state barrier heights, and resonance calculations,/. Chem. Phys. 81 309 (1984). 

AE12 is the difference on energy between the adiabatic ground state Ei and the first adiabatic excited state E2. 

The current model for ESIPT holds that optical excitation leads directly to a vibrational level of some adiabatic excited state. This state is the result of strong interactions between the initial and proton-transferred forms of the excited molecule. Its fluorescence may, in principle, have dual character. A weak component of normal Stokes shift should reflect the relative weight of the primary form for the emitting vibronic states, while the stronger fluorescence with large Stokes shift is attributed to the dominance of the final form. The reaction enthalpy in the excited state controls the duality of fluorescence. For a non-zero reaction enthalpy, the reaction occurs without a significant energy barrier. 

Time dependence of the excited state population by the pump pulse is shown in Fig. 5.18. Initial wavefunction is the vibrational ground state of the electronic ground state. The diabatic excited state population P2 is shown as solid curve (a), and the adiabatic excited state population Pa is shown as dashed (b). Also shown is the bound population Pbound = P +P2=Px+Pa- Part of the wavepacket damped by the optical potential... 

Fig. 5.27 (a) Time evolution of adiabatic excited state population formed by the pump... 

It is obvious that the lowest excited state in the initial geometry range (of the short OH distance) is tt — tt state. On the other hand, the lowest excited state in the right-hand side potential basin (beyond the potential barrier and of a longer OH distance) is of the Rydberg-state nature. More precisely, the main electronic configuration of the four low-ljdng (adiabatic) excited states beyond the potential barrier are... 

Wiberg KB, Wang Y-G, de Oliveira AE, Perera SA, Vaccaro PH (2005) Comparison of CIS and EOM-CCSD-calculated adiabatic excited states structures. Change in charge density on going to adiabatic excited states. J Phys Chan 109 466-477... 

The tautomerization at room temperature is caused by photoinduced proton transfer and due to the large distance between O and N atoms it cannot proceed intramoleculary. The process is solvent assisted as seen from the measured emission spectra in different solvents [53] in apolar or nonprotic polar solvents only the emission coming from 2 IE is detected, while in hydrogen-bonded solvents (alcohols or water for instance) a new strongly Stokes-shifted band appears in addition. This new band has been attributed to emission by a phototautomer 21K, formed by an adiabatic excited state intramolecular proton transfer (ESIPT) process in a complex between the excited enol form and solvent molecules [54, 55] (Figure 12.10). 

---