Coherence effects

Wynne K and Hochstrasser R M 1993 Coherence effects in the anisotropy of optical experiments Chem. Phys. 171 179-88... 

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). 

Just as above, we can derive expressions for any fluorescence lifetime for any number of pathways. In this chapter we limit our discussion to cases where the excited molecules have relaxed to their lowest excited-state vibrational level by internal conversion (ic) before pursuing any other de-excitation pathway (see the Perrin-Jablonski diagram in Fig. 1.4). This means we do not consider coherent effects whereby the molecule decays, or transfers energy, from a higher excited state, or from a non-Boltzmann distribution of vibrational levels, before coming to steady-state equilibrium in its ground electronic state (see Section 1.2.2). Internal conversion only takes a few picoseconds, or less [82-84, 106]. In the case of incoherent decay, the method of excitation does not play a role in the decay by any of the pathways from the excited state the excitation scheme is only peculiar to the method we choose to measure the fluorescence (Sections 1.7-1.11). 

How well do these quantum-semiclassical methods work in describing the dynamics of non-adiabatic systems There are two sources of errors, one due to the approximations in the methods themselves, and the other due to errors in their application, for example, lack of convergence. For example, an obvious source of error in surface hopping and Ehrenfest dynamics is that coherence effects due to the phases of the nuclear wavepackets on the different surfaces are not included. This information is important for the description of short-time (few femtoseconds) quantum mechanical effects. For longer timescales, however, this loss of information should be less of a problem as dephasing washes out this information. Note that surface hopping should be run in an adiabatic representation, whereas the other methods show no preference for diabatic or adiabatic. 

Fig. 21 a, b. DQT in a spin system with two magnetically equivalent 1=1 nuclei (Cu(sal)2, Ref. 62) EPR observer mF = 0. a) Weak pumping field B2 (0.02 mTrot). Only SQT are observed, b) Strong pumping field B2 (0.5 mTrol). Four DQT (marked by arrows) are observed. SQT are split by coherence effects... 

Vamavski OP, Ostrowski JC, Sukhomlinova L, Twieg RJ, Bazan GC, Goodson T (2002) Coherent effects in energy transport in model dendritic structures investigated by ultrafast fluorescence anisotropy spectroscopy. J Am Chem Soc 124 1736-1743... 

Conversely, we may observe an exceedingly narrow spectral line, so that o(x ) is approximated by <5(x ). Now the data i(x) represent the response function. This principle can, in fact, be used to determine the response function of a spectrometer. The laser, for example, is a tempting source of monochromatic radiation for measuring the response function of an optical spectrometer. Coherence effects, however, complicate the issue. We present further detail in Section II of Chapter 2. 

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]

Purely Rotational Coherence Effect and Time-Resolved Sub-Doppler Spectroscopy of Large Molecules, P. M. Felker, J. S. Baskin, and A. H. Zewail, J. Chem. Phys. 86,2460 and 2483... 

Finally, Mahon etal.5 have observed that even at frequencies as low as 670 MHz that ionization of Na occurs at fields near 1/3n5. At such low frequencies it is impossible to explain the ionization on the basis of incoherent single cycle Landau-Zener transitions. Rather the coherent effect of many cycles of the field is required. 

Motivated by the growing interest in high-order correlation functions, we develop in the present Paper a systematic approach to full statistics of charge transport in Andreev interferometers. We adopt several simplifying assumptions, which enables us to present an analytical solution for the CGF and, without a loss of generality, to clearly demonstrate essential features of coherent effects in the current statistics in NS structures. Our approach is based on the extended Keldysh-Green technique [13, 14], in which the CGF is determined by the equation... 

The first volume contained nine state-of-the-art chapters on fundamental aspects, on formalism, and on a variety of applications. The various discussions employ both stationary and time-dependent frameworks, with Hermitian and non-Hermitian Hamiltonian constructions. A variety of formal and computational results address themes from quantum and statistical mechanics to the detailed analysis of time evolution of material or photon wave packets, from the difficult problem of combining advanced many-electron methods with properties of field-free and field-induced resonances to the dynamics of molecular processes and coherence effects in strong electromagnetic fields and strong laser pulses, from portrayals of novel phase space approaches of quantum reactive scattering to aspects of recent developments related to quantum information processing. 

Glass-Maujean, M. and Beswick, J.A. (1989). Coherence effects in the polarization of photofragments, J. Chem. Soc., Faraday Trans. 2 85, 983-1002. 

The next two chapters are devoted to ultrafast radiationless transitions. In Chapter 5, the generalized linear response theory is used to treat the non-equilibrium dynamics of molecular systems. This method, based on the density matrix method, can also be used to calculate the transient spectroscopic signals that are often monitored experimentally. As an application of the method, the authors present the study of the interfadal photo-induced electron transfer in dye-sensitized solar cell as observed by transient absorption spectroscopy. Chapter 6 uses the density matrix method to discuss important processes that occur in the bacterial photosynthetic reaction center, which has congested electronic structure within 200-1500cm 1 and weak interactions between these electronic states. Therefore, this biological system is an ideal system to examine theoretical models (memory effect, coherence effect, vibrational relaxation, etc.) and techniques (generalized linear response theory, Forster-Dexter theory, Marcus theory, internal conversion theory, etc.) for treating ultrafast radiationless transition phenomena. 

In the resistivity curve for x = 0.05, the Cr-type of anomaly, pointing to the possible presence of a spin density wave below 5.8. K, is clearly visible. At higher x-values, the resistivity increases towards lower temperatures, with, for the x = 0.15 compound, a maximum around 5 K which is, with reference to other heavy-fermion compounds like, for instance, UBei3, considered to be caused by coherence effects. 

Baskin, J.S., Felker, P.M. and Zewail, A.H. (1987). Purely rotational coherence effect and time-resolved sub-Doppler spectroscopy of large molecules. II. Experimental, J. Chem. Phys., 86, 2483-2499. 

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