Excitation near-resonant

Excitation near resonance converts longitudinal magnetization M into the transverse magnetization Mxy according to... 

The Goeppert-Mayer two- (or multi-) photon absorption, mechanism (ii), may look similar, but it involves intennediate levels far from resonance with one-photon absorption. A third, quasi-resonant stepwise mechanism (iii), proceeds via smgle- photon excitation steps involvmg near-resonant intennediate levels. Finally, in mechanism (iv), there is the stepwise multiphoton absorption of incoherent radiation from themial light sources or broad-band statistical multimode lasers. In principle, all of these processes and their combinations play a role in the multiphoton excitation of atoms and molecules, but one can broadly... 

Robinson and Frosch<84,133> have developed a theory in which the molecular environment is considered to provide many energy levels which can be in near resonance with the excited molecules. The environment can also serve as a perturbation, coupling with the electronic system of the excited molecule and providing a means of energy dissipation. This perturbation can mix the excited states through spin-orbit interaction. Their expression for the intercombinational radiationless transition probability is... 

These observations implicating the role of zeaxanthin in the formation of the 535 nm band have prompted us to test the nature of this absorption feature using the resonance Raman excitation near its maximum (argon line at 528.7 nm). Figure 7.11a presents the v, resonance Raman spectral... 

The first two terms in (5) are called D-terms or dipolar terms, which are nonzero only if Ape =/= 0. The two-photon resonance denominator, ( leg — 2hco), indicates that an electron is excited into the lower excited state e. If we consider a near resonance condition hco = %imaginary part of the D-terms can be written in SI units as ... 

As we have seen, an external plane wave can excite resonances of a particle, which leads to significant variation in fluorescence intensity. A fluorescent molecule located in or near a particle can also excite the resonances of the particle. This can be modeled by again considering the molecule as a classical point dipole and obtaining the fields due to the dipole from the solution to the boundary value problem. 

Very large rate constants have been found for near resonant energy transfer between infrared active vibrations in CO2 Such near-resonant transitions and their dependence on temperature have also been studied for collisions between vibrationally excited CO2 and other polyatomic molecules as CH4, C2H4, SF et al. The deactivation cross-sections range from 0.28 for CH3F to 4.3 for SFs at room temperature, and decrease with increasing temperature. 

Laser irradiation onto the insulating (EDO)2PF6 crystal induces a phase transition to the highly conductive state within a few picoseconds [162, 180]. The crystal surface was excited by laser irradiation with a pulse width of 0.12 ps. The excitation photon energy (1.55 eV) was nearly resonant to the CT band at 11.1 x 10 cm (1.37 eV), directly reflecting the excitation of the charge ordered state. 

Radiationless excitation transfer occurs only when (D + A) initial state is in or near resonance with (D +A ) final state and there is a suitable donor-acceptor interaction between them. The rate of transfer, kt> a. is given by the time-dependent perturbation theory,... 

The vibrational overlap is both important and difficult to guess. In polyatomic molecules the large number of excited states near resonance will tend to increase the rates of all nonradiative processes, including decay to both A and B. However, intuition tells us that in a very large molecule not all vibrational levels will be important. For example, fluorescence lifetimes of alkyl derivatives of aromatic hydrocarbons are essentially independent of the length of the attached alkyl chain.26... 

Basco and Norrish25 flash photolyzed C2N2 and BrCN in the presence of NO and observed vibrationally excited nitric oxide. They suggested that it was formed through near-resonance vibration-vibration energy exchange with CN radicals and/or in the photolysis of NCNO. 

The steady state OH concentration in the atmosphere has been measured by the fluorescence technique using a dye laser tuned near 2820 A [Wang and Davis (1006), Davis ct al. (267)] or a microwave excited OH resonance lamp [Anderson (42)]. 

The electronic excitation discussed up to this point involves translational to electronic energy transfer. Of great practical importance is near-resonant electronic excitation-energy transfer, which leads to ion lasers in the He-Kr and Ne-Xe systems.294 The reactions involved are (He and Ne ... 

The interactions between metastable noble-gas atoms and ground-state noble-gas atoms are relatively simple and have been investigated quite extensively. If the excitation energy is lower than the ionization potential of the collision partner, the only important inelastic process is the transfer of excitation energy.12 The excitation transfer is usually very efficient when the process is near resonant. The process that is responsible for the operation of the He-Ne laser,13... 

As pointed out by Edmonds and Starace,12,13 the atoms are excited near the origin and can only escape in the z directions. The motion in the x,y plane is bound and is most likely to be the source of the quasi Landau resonances. To find the locations of the resonances it is adequate to ignore the z motion entirely and simply compute the energy spectrum of the motion in x,y plane. Applying the Bohr-Sommerfeld quantization condition leads to... 

Comparison of the collision numbers given above for vibration-vibration transfer with those for vibration-translation, given in Section 4, shows that in many cases vibration-vibration transfer between two resonant or near-resonant modes is much more efficient than vibration-translation transfer from either. This applies equally to homomolecular and heteromolecular collisions, and carries the interesting consequence that the quickest route for vibrational excitation of upper levels from the ground level by homomolecular collisions is an initial vibration-translation excitation to the v = 1 level, followed by successive vibration-vibration transfers to higher levels. Because of the selection rule, Av = 1,... 

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