Transition, fluorescence

Figure 8.29 X-ray fluorescence transitions forming (a) a K emission spectrum and (b) an L emission spectrum. The energy levels are not drawn to scale...

The absorption and emission spectra of a fluorophore are bands spread over a range of wavelengths with at least one peak of maximal absorbance and emission that corresponds to the So-Si and Si—S0 transitions, respectively. There are several vibrational levels within an electronic state and transitions from one electronic to several vibrational states are potentially possible. This determines that the spectra are not sharp but consist of broad bands. The emission spectrum is independent of the excitation wavelength. The energy used to excite the fluorophore to higher electronic and vibrational levels is very rapidly dissipated, sending the fluorophore to the lowest vibrational level of the first electronic excited state (Si) from where the main fluorescent transition occurs [3] (see Fig. 6.1). 

Selectivity is obtained by tuning the NH excitation laser to a specific rotational transition and following specific fluorescence transitions. Detection limits of 5 ppt for... 

In Table 22 the 0-0-fluorescence transition energy Es is given together with other parameters of excited helicenes. 

Fig.l. (a) Absorption and fluorescence of PPV at 1.4K, the dotted line shows the spectrum of an excitation pulse (centered at 2.292eV), 1° and le label the bimodal fluorescence transition (b) Scheme of the experimental set-up (S) Sample, (LI, L2) Lenses, (Mono) Monochromator, (PM) Photomultiplier, (PC) Peltier-Cooler, (Amp) Amplifier, (Ct) Counter, (Comp) Computer... 

We have seen earlier that Eu3+ possess two resonance levels, Do mid 5Z>i, from which fluorescence transitions to the J manifold of 1F takes place. The 5Do - 7Fo transition is strictly forbidden for regular octahedral symmetry but is observed in some complexes due to the lack of centro-symmetry. The intensity of the fluorescence transition is not directly dependent only on the amount of T 4f energy transfer, but mainly on the transition probabilities from a particular resonance level to the various J manifolds. However, the transition probabilities are sensitive functions depending on the ligand. A schematic representation of the... 

The fluorescence of ribonuclease solutions has been studied extensively by Cowgill. The absence of tryptophan permits the tyrosine fluorescence to be observed. The tyrosine fluorescence of RNase is very low in comparison with the maximum expected from its tyrosine content. All methods of denaturing RNase lead to an increase in fluorescence. Transitions, as indicated by the pattern of fluorescence change vs. denaturant concentration, are about the same as those indicated by other physical techniques [see, e.g., Gaily and Edelman (305) ]. 

Chamberlain and Simons (26) have shown by theory that when the absorption transition moment in H2O is parallel to the molecular plane, the degree of polarization P is (-1/13), if the OH fluorescence transition moment is perpendicular to the internuclear axis, and P is (1/7) if it is parallel to the internuclear axis. Simons and Smith (27) and MacPherson and... 

A CCD Raman spectrometer coupled with a 10-mW He-Ne laser has been used to eliminate fluorescence because the long-wavelength excitation by the He-Ne laser is not as likely to cause fluorescent transitions (71). Because of its directional property, coherent anti-Stokes Raman scattering (CARS) is also effective in avoiding fluorescence interference (see CARS in Section 3.9). 

Calibration of the pressure is best accomplished using the Ruby scale. Generally this is done using a metal gasket between the two diamond windows surrounding the sample in which a liquid (such as Nujol or Teflon oil) is added to produce hydrostatic pressure. The technique measures the pressure dependence of the sharp Ruby Ri fluorescence transition at 692.8 nm, although the R2 band at 694.2 nm can also be used. The Ruby fluorescence is induced by the blue excitation of the Ar+ (488.0 nm) or the He- C d (441.6nm) lasers. 

QMSTAT has to date been applied in a number of studies since its original formulation [19,20,21,85,120,121,122,139,161,162,163,164,165,166], These involve studies of ground state solvation, with geometry optimizations in a water solvent and solvation of ions also, solvent shift distributions have been computed for a number of different one-photon absorption and fluorescence transitions. We will not review all these studies, instead three noteworthy applications of QMSTAT are highlighted below. We start with a study of the solvation of the monatomic ions Li+, Na+, F and Cr, with special focus on the coupling between repulsion and the electronic degrees... 

Figure 9-5. The solvent shift distributions for (a) the two absorption transitions and (b) the two fluorescence transitions in indole at the air-water interface...

Figure 11.41. Energy level diagrams and transitions for two different F-branch transitions in the YS molecule. The broken lines denote laser-induced fluorescence transitions, whilst the continuous lines indicate radiofrequency double resonance transitions observed in rotational levels of the ground electronic state [82].

The fluorescence spectrum is independent of the wavelength of absorbed light (within limits), since the fluorescence transition is from E downward, whatever higher level such as D was reached on light absorption. 

The peak observed at a Raman shift of 1550cm can be assigned to a fluorescence transition from the B2u electronic excited state with De(v — = 1)... 

Figure 3 Plots of free energy of zero-order precursor and successor states versus reaction coordinate, for electron-transfer reactions / (A+- B) — r(A- B+). (a) AG° > 0 (b) AG° = 0 (c) 0 > AG° > —X (d) AG° < —X. The upward-pointing arrows in (a), (b), and (c) indicate intervalence charge-transfer transitions the downward-pointing arrow in (d) indicates a possible fluorescent transition from the precursor state / (A+- -B)...

---