Electron coherent

Wynne K and Hochstrasser R M 1995 Anisotropy as an ultrafast probe of electronic coherence in degenerate systems exhibiting Raman scattering, fluorescence, transient absorption and chemical reactions J. Raman Spectrosc. 26 561-9... 

Stueckelberg derived a similar fomiula, but assumed that the energy gap is quadratic. As a result, electronic coherence effects enter the picture, and the transition probability oscillates (known as Stueckelberg oscillations) as the particle passes through the non-adiabatic region (see [204] for details). 

Note that the usage of 10-fs laser pulse leads to rich oscillatory components as well as these rapid kinetics in their pump-probe time-resolved profiles. Obviously in this timescale, the temperature T will have no meaning except for the initial condition before the pumping process. In addition, such oscillatory components may be due not only to vibrational coherence but also to electronic coherence. A challenging theoretical question may arise, for such a case, as to how one can describe these ultrafast processes theoretically. 

Recently, Scherer et al. have used the 10-fs laser pulse with A,excitation = 860 nm to study the dynamical behavior of Rb. Sphaeroides R26 at room temperatures. In this case, due to the use of the 10-fs pulse both P band and B band are coherently excited. Thus the quantum beat behaviors are much more complicated. We have used the data given in Table I and Fig. 19 to simulate the quantum beat behaviors (see also Fig. 22). Without including the electronic coherence, the agreement between experiment and theory can not be accomplished. 

A measure for the electronic coherence of the wave function are the nondiagonal elements of the electronic density matrix, which, for example, in the diabatic representation are given by (k k )... 

Finally, we consider the performance of the MFT method for nonadiabatic dynamics induced by avoided crossings of the respective potential energy surfaces. We start with the discussion of the one-mode model. Model IVa, describing ultrafast intramolecular electron transfer. The comparison of the MFT method (dashed line) with the quantum-mechanical results (full line) shown in Fig. 5 demonstrates that the MFT method gives a rather good description of the short-time dynamics (up to 50 fs) for this model. For longer times, however, the dynamics is reproduced only qualitatively. Also shown is the time evolution of the diabatic electronic coherence which, too, is... 

Let us begin with the one-mode electron-transfer system. Model IVa, which still exhibits relatively simple oscillatory population dynamics [205]. SimUar to what is found in Fig. 5 for the mean-field description, the SH results shown in Fig. 13 are seen to qualitatively reproduce both diabatic and adiabatic populations, at least for short times. A closer inspection shows that the SH results underestimate the back transfer of the adiabatic population at t 50 and 80 fs. This is because the back reaction would require energetically forbidden electronic transitions which are not possible in the SH algorithm. Figure 13 also shows the SH results for the electronic coherence which are found to... 

Figure 6.10 Ultrafast efficient switching in the five-state system via SPODS based on multipulse sequences from sinusoidal phase modulation (PL). The shaped laser pulse shown in (a) results from complete forward design of the control field. Frame (b) shows die induced bare state population dynamics. After preparation of the resonant subsystem in a state of maximum electronic coherence by the pre-pulse, the optical phase jump of = —7r/2 shifts die main pulse in-phase with the induced charge oscillation. Therefore, the interaction energy is minimized, resulting in the selective population of the lower dressed state /), as seen in the dressed state population dynamics in (d) around t = —50 fs. Due to the efficient energy splitting of the dressed states, induced in the resonant subsystem by the main pulse, the lower dressed state is shifted into resonance widi die lower target state 3) (see frame (c) around t = 0). As a result, 100% of the population is transferred nonadiabatically to this particular target state, which is selectively populated by the end of the pulse.

The pre-pulse thus prepares the system in a state of maximum electronic coherence (see Figure 6.10b around t = -100 fs). Only 0.5% of the population escapes to the resonant target state 4). Transitions to the off-resonant target states 3) and 5) are completely suppressed since the dynamic Stark splitting of the... 

Femtosecond photon echo measurements of electronic coherence relaxation of I2 in the presence of He, Ar, N2,02, C3H8... 

Photon Echo (PE) and Reverse Transient Grating (RTG) measurements of the loss of electronic coherence between the X( 2g+) and B(3FIou+) states of molecular iodine are measured by three pulse four wave mixing (FWM). Two cases are considered, relatively low pressure isolated iodine (1-2 Torr), and iodine at high pressure (>10torr) or in the presence of several hundred Torr of buffer gas. 

In Ref. [4] we have studied an intense chirped pulse excitation of a molecule coupled with a dissipative environment taking into account electronic coherence effects. We considered a two state electronic system with relaxation treated as diffusion on electronic potential energy surfaces with respect to the generalized coordinate a. We solved numerically equations for the density matrix of a molecular system under the action of chirped pulses of carrier frequency a> with temporal variation of phase [Pg.131]

G. Gerber In response to Prof. Mukamel, I should remark that the coherence between molecular electronic states induced by our intense ultrashort laser pulse is not restricted to bound states but also includes repulsive electronic surfaces. In that sense chemical bonding is related to electronic coherence. 

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