Emission resulting from excited

Intense sodium D-line emission results from excited sodium atoms produced in a highly exothermic step (175). Many gas-phase reactions of the alkafl metals are chemiluminescent, in part because their low ioni2ation potentials favor electron transfer to produce intermediate charge-transfer complexes such as [Ck Na 2] (1 )- There appears to be an analogy with solution-phase electron-transfer chemiluminescence in such reactions. 

Depending on excitation wavelength either of two emission spectra may be observed (Fig. 3). The twin peaks at 690.5 nm and 692.2 nm represent long lived emission resulting from excitation of the sapphire matrix plate and are useful fiducial markers. 

The reaction of samarium and NF3 shows strong chemiluminescence. The emission results from excited SmF molecules and Sm atoms. The highest photon yield measured (for the definition, see the AI + NF3 reaction) was 70% at 2.3 Torn About 12% of the reaction exothermi-city was converted into radiation [8]. 

A series of complexes of platinum(ll) containing cyanide and a-diimine ligands have been prepared that have intense emissions in the 560-715-nm range. These complexes have the formulae Pt(LL)(CN)2 or [Pt(LL)2][Pt(CN)4], and they all have a close intermetallic separation between the platinums of approximately 3.3 A. The ambient temperature emission maxima and lifetimes are collected in Table 3.6. This emission results from excitation due to a metal to ligand charge transfer (MLCT) transition of type da dz ( )) n (a-diimine). Metal-metal... 

C07-0126. The series of emission lines that results from excited hydrogen atoms undergoing transitions to the n — 3 level Is called the Paschen series. Calculate the energies of the first five lines In this series of transitions, and draw an energy level diagram that shows them to scale. 

Finally, A is the output gray value after the acceptor channel9 scaling (g3) of the fraction of acceptor fluorescence in the acceptor channel (FJ), which depends on the acceptor quantum yield (Qa) and on the amount of acceptors NA excited at a x (t il A ), of (usually very minor) contributions of donor fluorescence cross-excited at and leaking into the acceptor channel ((No — ENs)fa< -DQdF d F) and of sensitized emission resulting from cross-excitation at 2 x (ENs dQaF 3) However, as... 

The brilliant emissions resulting from the oxidation of certain oxalic acid derivatives, especially in the presence of a variety of fluorophores, are the bases of the most active area of current interest in CL. This group of chemiluminescent reactions has been classified as peroxyoxalate chemistry because it derives from the excited states formed by the decomposition of cyclic peroxides of oxalic acid derivatives called dioxetanes, dioxetanones, and dioxetanediones. 

Eximer Fluorescence. Since Forster and Kasper discovered concentration-dependent long-wavelength emission resulting from association of an electronically excited pyrene molecule with another ground state pyrene molecule,39 the phenomenon of excimer fluorescence has been studied extensively.40 The mechanism for excimer formation and emission can be represented by... 

Sulfur Dioxide. Both flame photometric and pulsed fluorescence methods have been applied to the continuous measurement of S02 from aircraft. In the flame photometric detector (FPD), sulfur compounds are reduced in a hydrogen-rich flame to the S2 dimer. The emission resulting from the transition of the thermally excited dimer to its ground state at 394 nm is measured by using a narrow band-pass filter and a photomultiplier tube. 

Banded optical emission results from electronically excited nitric oxide. The y and /S bands are often observed. Furthermore, chemiluminescence results from the well-studied step... 

Unprimed, solid-line curves are photocurrent (left-hand scale) and primed, dotted-line curves are emission intensity (right-hand scale) monitored at Kmax 600 nm. Curves A and A result from excitation at 501.7-nm, 23°C Curves B and B from 514.5-nm, 23< C Curves C and C , 49°C and 501.7-nm excitation Curves D and D 86°C, 514.5-nm irradiation. Note that the ordinate of Curve D has been expanded by a factor of 10. Equivalent numbers of 501.7- and 514.5-nm photons were used to excite the photoelectrode in identical geometric configurations. The exposed electrode area is 0.41 cm2, corresponding to an estimated x for 501.7-nm excitation at 23°C and +0.7 V vs. Ag (PRE) of 0.50, uncorrected for solution absorbance and reflectance losses (9). 

Figure 6d shows the comparison of this spectrum with the theoretical one. The straight lines are the theoretical emission lines from the excited HCHO calculated by Toby [27]. As the peak wavelengths and the intensities for the fine spectra agree with the theoretical lines, we can concluded that the CTL emission results from the excited HCHO produced in the course of... 

Electronically excited NO has been observed as a product of the reaction of ground state oxygen atoms with nitric oxide. In the first [447], the emission results from the two-body radiative recombination reaction... 

Figure 15 The kinetic scheme illustrating the interplay between exciton (S) and charge carrier (q) trapping by crystal defects (S0t)-The PL spectrum of the crystal contains the excitonic emission (kr, hvm) and the trap center emission (kj., hi ). the latter being controlled by the number of the defect sites available for excitation. The exciton capture process (yst) competes directly with charge carrier trapping (yqt). The defects filled with charge reduce the emission resulting from radiative relaxation of the excited states produced at defect sites. For further explanations, see text.

The photoluminescence of dipyridophenazine complexes of ruthenium ) in the presence and absence of DNA has been well-characterized (38-40, 46-52). Excitation of the dppz complexes with visible light (440 nm) leads to localized charge transfer from the metal center (39, 40). In aqueous solution, the emission resulting from the metal-to-ligand charge-transfer excited state is deactivated via nonradiative energy transfer... 

From the results of a high-resolution study of the CN chemiluminescence, Iwai, Savadatti, and Broida [151] proposed that reactions (79) and (80) should be reserved to explain the high-energy tail bands, which extend to A 2ri(i/ = 24) and B 22+(u = 15), and that Bayes P1 emission from low levels in A 2II probably results from excitation in the reactions... 

Photodecomposition. As reviewed by Cundall and Davies (61), both of these absorption systems have been studied, and product yields resulting from excitation from 435.8 to 238 nm have been reported (22,30,176). Since the last review by Cundall and Davies (61), most studies have dealt with the A X system, since both singlet and triplet emission have provided valuable tools in the exploration of biacetyl photochemistry (see ref. 185). Three photodecomposition processes have been proposed for biacetyl ... 

In this case, the K s are the intersystem crossing rate constants. A detailed description of the different experimental techniques used at the present time, together with equations derived for molecules whose emission results from two zf levels, is given in a recent review of the subject (87). In this section we will give only a brief description of these PMDR methods. In all but the pulsed-excitation method, these assumptions are made (a) the spin-lattice relaxation is absent and (b) the microwave radiation either saturates or inverts the population of... 

Figure 2 Experimental arrangement for measurements of the Fe nuclear resonance at the Advanced Photon Source (APS). In the standard fill pattern, electron bunches with a duration of 100 ps are separated by 153 ns. X-ray pulses are generated when alternating magnetic fields in the undulator accelerate these electron bunches. The spectral bandwidth of the X-rays is reduced to 1 eV by the heat-load monochromator and to 1 meV by the high-resolution monochromator. At the sample, the flux of the beam is about 10 photons/s. APD indicates the avalanche photodiode used to detect emitted X-rays. The lower right inset illustrates that counting is enabled only for times weU-separated from the X-ray pulse, so that only delayed photon emission resulting from decay of the nuclear excited state contributes to the experimental signal...

Another major chemical phenomenon related to ultrasonic cavitation is sonolumi-nescence, by which a tiny light is formed in a cool liquid. This form of light emission results from the high-temperature formation of reactive chemical species in excited electronic states. Emitted light from such states provides a spectroscopic probe for the cavitation effect. Some electrical and thermal theories on this phenomenon have been reported [25]. 

---