One-step excitation

The incorporation of 1,3-dibutylalloxazine (DBA) as an electron carrier in the vesicle wall increased the accumulation rate of the reduced disodium 9,10-anthraqui-none-2,6-disulfate (AQDSH2) by 7 times. In the system of Fig. 6, the electron is pumped up in two steps at the inside as well as outside of the vesicle wall, however, since the photoreaction centers (surfactant ZnP) are the same for both the walls, the amount of energy acquired by the two steps excitation is equal to that by one step excitation. The incorporation of different photoreaction centers inside and... 

Fig. 6. Schematic of mechanisms for accumulation of vibrational energy on a vibrator. DIMET refers to multiple one-step excitations, thus dominating when the excitation (dashed arrows) rates are comparable to decay rates. DIET refers to one step gain of several quanta. This mechanism is mediated by anharmonicities of the vibrational potential. In general, a transition of several quanta at once has lower probability, but since the total number of steps is so decreased, it dominates over a DIMET mechanism for sufficient low excitation rates.

Figure 10.5 Schematic of photocatalytic water splitting by one-step excitation in a single photocatalyst (0) light irradiation and absorption, (1) photo-excitation of electron-hole pairs, (2) migration of...

Different excitation schemes for LEI are shown in Figure 3. The simplest and most widely used is the one-step excitation scheme (Fig. 3 A). Elements with low ionization potential (mainly alkali metals) can be efficiently ionized by the one-step scheme with dye lasers in the visible range. For a number of elements (Cd, Mg, Pb. etc.) the one-step scheme can be efficient with... 

When the excited state 2) has been selectively populated by optical pumping with laser LI, transitions to still higher levels m) can be induced by a second tunable laser L2 (Fig. 10.14b). This two-step excitation may be regarded as the special resonance case of the more general two-photon excitation with two different photons hu)2 (Sect. 7.5). Because the upper levels m) must have the same parity as the initial level l), they cannot be reached by an allowed one-photon transition. The one-step excitation by a frequency doubled laser with the photon energy 2hu) = ft(wi+a>2) therefore excites, in the same energy range, levels of opposite parity compared to those levels reached by the two step excitation. 

In order to appreciate these and other results of yield spectroscopy on NEA diamond surfaces, it is best to recall briefly Spicer s three-step model of photoelectron emission, which is likely to be nowhere better suited than in the case at hand [109]. This model divides the photoelectron emission process up into three conceptually separate processes, (i) The bulk absorption of light generates photoexcited electrons and holes, and (ii) electrons travel to the surface with the possibility to suffer inelastic losses on their way before they (iii) escape into vacuum where they are being detected. In normal photoelectron spectroscopy interest lies in the so-called primary current, that is, in those electrons that leave the sample without energy loss on their way to the surface. In this case, the photoexcitation, transport, and escape processes are not entirely independent. For crystalline samples with well-ordered surfaces, the wave vector component parallel to the surface, k, is, for example, conserved from the initial electron state to the free electron in vacuum. In this case, a better description of the photoelectron emission is by a one-step excitation from an initial band structure state to a final state constructed as an inverse LEED state (Chapter 3.2.2). The inelastic mean free path of photoexcited electrons, is energy dependent and lies in the nanometer range (Chapter 3.2.3). 

The amount of computation for MP2 is determined by the partial transformation of the two-electron integrals, what can be done in a time proportionally to m (m is the number of basis functions), which is comparable to computations involved in one step of CID (doubly-excited configuration interaction) calculation. To save some computer time and space, the core orbitals are frequently omitted from MP calculations. For more details on perturbation theory please see A. Szabo and N. Ostlund, Modem Quantum Chemistry, Macmillan, New York, 1985. 

When Hammond and co-workers(59) found that the intersystem crossing quantum yield for aromatic ketones was unity (see Chapter 3) it was a short but very important step to realize that these compounds should be ideal triplet sensitizers. Thus one can excite the triplet state of molecules that otherwise would be formed inefficiently, if at all, by intersystem crossing. This idea resulted in a number of papers in the early 1960 s from the Hammond group on this topic. It is not possible in this short section to survey this area, but a few of the early studies are indicated by the following reactions ... 

We have now to go one step further and to build stellar evolution models where the transport of angular momentum will be followed self-consistently under the action of meridional circulation, shear turbulence, and internal gravity waves. In this path some important aspects still need to be clarified Can we better describe the excitation mechanisms and evaluate in a more reliable way the quantitative properties of the wave spectra What is the direct contribution of 1GW to the transport of chemicals, especially in the dynamical shear layer produced just below the convective envelope by the wave-mean flow interaction What is the influence of the Coriolis force on IGW How do 1GW interact with a magnetic field Work is in progress in this direction. 

For trace analysis in fluids, some Raman sensors (try to) make use of the SERS effect to increase their sensitivity. While the basic sensor layout for SERS sensors is similar to non-enhanced Raman sensors, somehow the metal particles have to be added. Other than in the laboratory, where the necessary metal particles can be added as colloidal solution to the sample, for sensor applications the particles must be suitably immobilised. In most cases, this is achieved by depositing the metal particles onto the surfaces of the excitation waveguide or the interface window and covering them with a suitable protection layer. The additional layer is required as otherwise washout effects or chemical reactions between e.g. sulphur-compounds and the particles reduce the enhancement effect. Alternatively, it is also possible to disperse the metal particles in the layer material before coating and apply them in one step with the coating. Suitable protection or matrix materials for SERS substrates could be e.g. sol-gel layers or polymer coatings. In either... 

A disposable, patterned, planar waveguide with a number of individual wells has been reported for a one-step homogeneous immunoassay of IgG.<133) The device is fabricated by an ion-exchange process, etching, and covalent reagent immobilization. The sample fills the waveguide by capillary action. The sample well, as well as fluorescent and nonfluorescent control wells are excited by an evanescent field, and individually scanned. The IgG detection limit is in the 10range. 

Sorokin and Lankard illuminated cesium and rubidium vapors with light pulses from a dye laser pumped by a ruby giant-pulse laser, and obtained two-step excitation of Csj and Rbj molecules (which are always present in about 1 % concentration at atomic vapor pressures of 10" - 1 torr) jhe upper excited state is a repulsive one and dissociates into one excited atom and one ground-state atom. The resulting population inversion in the Ip level of Cs and the 6p level of Rb enables laser imission at 3.095 jum in helium-buffered cesium vapor and at 2.254 pm and 2.293 /zm in rubidium vapor. Measurements of line shape and frequency shift of the atomic... 

However, this is in general a quite impractical method, as it requires the iterative series of dress-then-diagonalize steps to get convergence for each individual state. Moreover, even if no particular numerical problems arise in the case of states that are not dominated by one particular excitation, the method does not seem to be well-adapted from a formal point of view to such cases because they do not satisty the condition stated in eq. (2). Notwithstanding, this procedure can be practical for the calculation of outer-valence ionization potentials of closed-shell molecules. In such cases, one must to deal with the doublet states of the cation that are well dominated by a unique Koopmans determinant. 

In the decay chain of let Ni = N2 = Th, and /V3 = Pa, derive how the concentration of /V3 would change with time. You may ignore different excitation states of Pa, and simplify the decay of Pa as one-step decay to with a half-life of 1.1 7 min. 

If we consider now transfer between two identical ions the same considerations can be used. If transfer between S ions occurs at a high rate, in a lattice of S ions there is no reason why the transfer should be restricted to one step. This can bring the excitation energy far from the site where the absorption took place. If in this way, the excitation energy reaches a site where it is lost nonradiatively (quenching site), the luminescence will be quenched. This phenomenon is called concentration quenching. 

Phthalocyanines 392 are porphyrin analogues embellishing Nature with exciting colours. Their pentamer 393 obtained in a one-step reaction has a cavity, thus it can play the role of host [12]. 

One-step processes occur whenever the stochastic process consists of the absorption or emission of photons or particles, the excitation and deexcitation of atoms or nuclei, or of electrons in semiconductors, the birth and... 

Several attempts have been made to devise simpler optimization methods than the lull second order Newton-Raphson approach. Some are approximations of the full method, like the unfolded two-step procedure, mentioned in the preceding section. Others avoid the construction of the Hessian in every iteration by means of update procedures. An entirely different strategy is used in the so called Super - Cl method. Here the approach is to reach the optimal MCSCF wave function by annihilating the singly excited configurations (the Brillouin states) in an iterative procedure. This method will be described below and its relation to the Newton-Raphson method will be illuminated. The method will first be described in the unfolded two-step form. The extension to a folded one-step procedure will be indicated, but not carried out in detail. We therefore assume that every MCSCF iteration starts by solving the secular problem (4 39) with the consequence that the MC reference state does not... 

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