Transition the excited

Category 1, Simple Cleavage into Radicals.Aldehydes and ketones absorb in the 230-330-nm region. This is assumed to result from an n—>tt singlet-singlet transition. The excited aldehyde or ketone can then cleave. ... 

This chapter deals mainly with (multi)hyphenated techniques comprising wet sample preparation steps (e.g. SFE, SPE) and/or separation techniques (GC, SFC, HPLC, SEC, TLC, CE). Other hyphenated techniques involve thermal-spectroscopic and gas or heat extraction methods (TG, TD, HS, Py, LD, etc.). Also, spectroscopic couplings (e.g. LIBS-LIF) are of interest. Hyphenation of UV spectroscopy and mass spectrometry forms the family of laser mass-spectrometric (LAMS) methods, such as REMPI-ToFMS and MALDI-ToFMS. In REMPI-ToFMS the connecting element between UV spectroscopy and mass spectrometry is laser-induced REMPI ionisation. An intermediate state of the molecule of interest is selectively excited by absorption of a laser photon (the wavelength of a tuneable laser is set in resonance with the transition). The excited molecules are subsequently ionised by absorption of an additional laser photon. Therefore the ionisation selectivity is introduced by the resonance absorption of the first photon, i.e. by UV spectroscopy. However, conventional UV spectra of polyatomic molecules exhibit relatively broad and continuous spectral features, allowing only a medium selectivity. Supersonic jet cooling of the sample molecules (to 5-50 K) reduces the line width of their... 

For the d-d transitions the excited states arise from the (a2 7r 52) and (on 3) configuration, but separate designations are not given since many of the levels are appreciably mixed by configuration interaction. 

The excited state is formed out of a combination of 2p orbitals, and the absorption spectrum is seen as a Is-1 2p transition. The excited state is weakly bound in this model, by 0.9 eV. The calculated oscillator strength is too low, which seems to be a feature of all structural models. There is no configurational... 

The electronic structure of fluorenes and the development of their linear and nonlinear optical structure-property relationships have been the subject of intense investigation [20-22,25,30,31]. Important parameters that determine optical properties of the molecules are the magnitude and alignment of the electronic transition dipole moments [30,31]. These parameters can be obtained from ESA and absorption anisotropy spectra [32,33] using the same pump-probe laser techniques described above (see Fig. 9). A comprehensive theoretical analysis of a two beam (piunp and probe) laser experiment was performed [34], where a general case of induced saturated absorption anisotropy was considered. From this work, measurement of the absorption anisotropy of molecules in an isotropic ensemble facilitates the determination of the angle between the So Si (pump) and Si S (probe) transitions. The excited state absorption anisotropy, rabs> is expressed as [13] ... 

The dye photosensitizers are excited from the ground state (S) to the excited state (S ) owing to the MLCT transition. The excited electrons are injected into the conduction band of the 2 film electrode, resulting in the oxidation of the dye photosensitizers. 

In Table 2 we summarize the results of the DDCI calculations on the lowest excitation energies for terrace, step and comer F and F+ centers. As expected, for a given transition the excitation energy decreases as the coordination of the defect decreases. For F centers, the allowed singlet to singlet lowest transition occurs at 3.4 eV for the surface, 2.9 eV for the step and 2.6 eV for the comer. The same trend is found for the F+ centers, where the first doublet to doublet transition, goes from 3.6 eV for the surface, to 2.6 eV for the step and 2.4 eV for the comer. As observed previously for the bulk calculations, excitations for the F+ centers appear around 0.2 eV below the excitations due to F centers. The excitations at the step and comer sites are shifted about 0.5-1.2 eV compared to... 

Molecules in the second coordination sphere, that is, solvent or partners of an ion pair, can transfer charge to the metal ion of a coordination complex in an optically induced electronic transition. The excited states are, respectively, known as solvent to metal charge transfer (SMCT) and ion pair charge transfer (IPCT) excited states. A typical example are the ion pairs, [Cora(NH3)6]3 +, X-, formed between [Coln(NH3)6]3 + and halide and pseudohalide ions X. The UV-Vis spectrum of ion... 

X 109 and 8. 9 x 109 s 1 for Ndm and Ybm, respectively. Both the above-described in-termolecular mechanism, as well as an intramolecular pathway in the ternary complex with aad which forms in solution, are responsible for the observation of NIR luminescence in these systems. Addition of water to the toluene solutions quenches the NIR luminescence, while it enhances the visible CL emission of the corresponding solution of Eum and Tbm (Voloshin et al., 2000c). Neodymium and ytterbium tris(benzoyltrifluoroacetonates) display the same CL as tta complexes, although for Ybm its intensity is about 2.5 times lower than for the tta chelate. On the other hand, almost no CL is detected for acetylacetonate complexes (Voloshin et al., 2000a). Thermal or photochemical decomposition of aad also triggers CL from [Pr(dpm)3] and Pr(fod)3], both in the visible (from the 3Pi, 3Po, and 1D2 levels) and in the NIR at 850 nm ( Do -> 3F2 transition) and 1100 nm ( D2 3F4 transition). The excited... 

Excitation conditions At about 10cm"1 and farther above the 0-0 transition, the excitation wavelength does not seem to influence the fluorescence spectrum. This observation points to a rapid thermalization of the exciton population.87 In contrast, the excitation power has an important nonlinear effect Above a threshold stimulated emission is observed on the 0-1400 line, at 23692 cm"1.88 The crystal behaves as an optical resonator, with laser effects, which explains the sharpness and the intensity of this line in Fig. 2.17.89... 

The basis set effects on the excitation energies are not uniform. For the first 2 valence transitions, the excitation energies decrease by 0.012 and 0.056 eV on going from aug-cc-pVDZ to aug-cc-pVTZ. For other transitions there is usually an increase in the excitation energy, often by more than 0.1 eV. The ANOl results tend to be between the aug-cc-pVDZ and aug-cc-pVTZ values, usually closer to the former. 

Photoionization can result either from the direct interaction of a photon with the ionizing electron or by an indirect process. An example of the latter is autoionization where a photon is absorbed to produce an excited state of the molecule, M, by a resonance transition. The excited state then subsequently decays to the molecular ion and a photoelectron (equation 4) ... 

Polar solvents affect the excited state differently in TT 7T and n -TT transitions. The excited state in TT TT transition is stabilized. A reduction in the energy gap will occur and the emission will be shifted to a longer wavelength (red shift). Therefore, the difference between excitation and emission wavelengths will be greater in polar solvents. 

If the maximum of the transition V (x) is displaced from the equilibrium position (x 0), the interaction induces a non-vertical transition. The excited wave packet 0) V(x)

i(x) is centered around... 

For any atomic multipole transition, the excited state can be described in terms of the dual representation of corresponding SU(2) algebra, describing the azimuthal quantum phase of the angular momentum. In particular, the exponential of the phase operator and phase states can be constructed. The quantum phase variable has a discrete spectrum with (2j + 1) different eigenvalues. 

Spin-free Fe(diimine)zX2 complexes show a weak broad band at 8.5—12.5 AK with two more or less clearly resolved components separated by ca. 2 AK. Kdnig et al. (33,34,40) associate this band with the 5X2 - transition, the excited E state being split by low symmetry field components. For spin-free l e(bipy)2(NCS)2 and Fe(phen)2(NCS)2, 10 Dj is estimated at 11.2 and 11.8AK, respectively. 

FIGURE 11.21 An example of a clock atomic transition. The excitation probability of the clock transition (the atomic oscillator) is measured through the quantum jump number vs. the laser tuning of the local oscillator. Each probe pulse is of 90 ms duration, and twenty probe cycles were performed for each value of the detuning. (Reproduced with the permission of the Physikalisch-Technisehe Bundesanstalt.)... 

Two-photon absorption can be formally described by a two-step process from the initial level i) via a virtual level v) to the final level /> (Fig. 2.30b). This fictitious virtual level is represented by a linear combination of the wave functions of all real molecular levels kn) that combine with i) and f) by allowed one-photon transitions. The excitation of w) is equivalent to the sum of all off-resonance excitations of these real levels kn). The probability amplitude for a transition i) v)... 

For a polar solute in polar solvents, dipole-dipole interactions will stabilize the ground state of the solute according to the polarity of the solvent. In this case the solvent molecules will be oriented around the ground-state dipole and, if the dipole moment is increased by the transition, the excited state will be stabilized more by more polar solvents (those with higher dielectric constants). The resulting red shift will again add to the general red shift compared to the gas phase. 

Due to the selection rule f =0, l, 2, 3 for three photon dipole transitions the excitation of a state is possible. As shown in the simplified potential diagram in fig. 3 two almost resonant intermediate steps (b ttCOJ) and ZTg ) are involved in the three photon excitation of the Rydberg states. This explains the comparatively strong appearance of the triplett bands and leads to the assumption that one of... 

The second step is the transition from the intermediate state to the final excited state in the LUMO ( Eex, el) <8> Eex ",phonon)) by the DP-CP or the free photon (conventional propagating light). Here, E x, el)) represents the excited state of the electron, and E x phonon) represents the excited state of a phonon whose energy depends on the photon energy used for the transition. Since this transition is electric dipole-allowed, it can be brought about not only by the DP-CP but also by the free photon. After this transition, the excited phonon relaxes to the thermal equilibrium state. E x iharma phonori)... 

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