Emitting species

Unstable monohaUdes of xenon ([16757-14-5], XeF [55130-03-5], XeCl [55130-04-6], XeBr and [55130-05-7], Xel), have been produced in the gas phase by electron bombardment methods (43,44) and in soHd matrices by gamma and ultraviolet inradiation methods (45,46). Although short-Hved in the gas phase, these haUdes are of considerable importance as light-emitting species in gas lasers (qv). 

Most likely singlet oxygen is also responsible for the red chemiluminescence observed in the reaction of pyrogaHol with formaldehyde and hydrogen peroxide in aqueous alkaU (152). It is also involved in chemiluminescence from the decomposition of secondary dialkyl peroxides and hydroperoxides (153), although triplet carbonyl products appear to be the emitting species (132). 

White Phosphorus Oxidation. Emission of green light from the oxidation of elemental white phosphoms in moist air is one of the oldest recorded examples of chemiluminescence. Although the chemiluminescence is normally observed from sotid phosphoms, the reaction actually occurs primarily just above the surface with gas-phase phosphoms vapor. The reaction mechanism is not known, but careful spectral analyses of the reaction with water and deuterium oxide vapors indicate that the primary emitting species in the visible spectmm are excited states of (PO)2 and HPO or DPO. Ultraviolet emission from excited PO is also detected (196). 

Apart from XeF, which is the light-emitting species in certain Xe/F2 lasers, there is no evidence for the existence of any odd-valent fluorides. Reports of XeFg have not been confirmed. Of the other halides, XeCl2, XeBr2 and XeCl4 have been detected by Mossbauer spectroscopy as products of the -decay of their... 

Bioluminescence of firefly luciferin can produce a wide range of colors when catalyzed by different luciferases obtained from various species of fireflies, with their emission maxima ranging from 535 nm (yellow-green) to 638 nm (red). Apparently, each spectrum is emitted from a single emitting species they are not the composites of the yellow-green peak and the red peak (Seliger and McElroy, 1964). 

If the emitting species is not a reaction-product molecule directly formed by the exergonic reaction (as is the case in the luminol reaction, for example), chemiluminescence can occur via energy transfer processes ... 

In the case of chemiluminescence occurring on treatment of di-benzanthrone with hypochlorite, as mentioned above, an endo peroxide might well be a key intermediate formed from 4 and singlet oxygen. The emitting species, however, is trichloro-dibenzanthrone, not 4 itself 70h... 

It has been established 106> that 3-aminophthalate is the emitting species in luminol chemiluminescence and that in all known cases of other cyclic hydrazides the corresponding dicarboxylate is the emitter (e.g. 97,107)). 

It is therefore suggested that the emitting species are the monoanion 115 in red, and the dianion 117 in yellow-green chemiluminescence. 

Lophine emits yellow CL upon oxidation by molecular oxygen in alkaline solution. The oxidation is believed to produce a free radical [3], which is further oxidized to a hydroperoxide, which is the light-emitting species [4-6], A number of chemiluminescent derivatives of lophine have been synthesized and have been shown to exhibit varying efficiencies of CL. Lophine has been used in the analysis of metal ions such as Co2+ that catalyze the chemiluminescent reaction between it and hydrogen peroxide [7], It has also been used as a chemiluminescent indicator in titrimetry [8],... 

Several N-methyl-9-acridinecarboxylic acid derivatives (e.g., 10-methyl-9-acridinecarboxylic chloride and esters derived therefrom [39]) are chemiluminescent in alkaline aqueous solutions (but not in aprotic solvents). The emission is similar to that seen in the CL of lucigenin and the ultimate product of the reaction is N-methylacridone, leading to the conclusion that the lowest excited singlet state of N-methylacridone is the emitting species [40], In the case of the N-methyl-9-acridinecarboxylates the critical intermediate is believed to be either a linear peroxide [41, 42] or a dioxetanone [43, 44], Reduced acridines (acridanes) such as N-methyl-9-bis (alkoxy) methylacridan [45] also emit N-methylacridone-like CL when oxidized in alkaline, aqueous solutions. Presumably an early step in the oxidation process aromatizes the acridan ring. 

Consideration should be given to the flow rate of the sample through the detection cell. Shultz and co-workers have demonstrated the wide variability in reaction kinetics between ECL reactions, and hence the influence of flow rate on ECL intensity [60], For example, the rate constants (k) of the Ru(bpy)32+ ECL reactions of oxalate, tripropylamine, and proline were calculated to be 1.482, 0.071, and 0.011/s, respectively. Maximum ECL emission was obtained at low linear velocities for slow reactions ranging up to high linear velocities for fast reactions. That is, the flow rate and flow cell volume should be optimized such that the light-emitting species produced is still resident within the flow cell, in view of the light detector, when emission occurs. 

The same authors studied the CL of 4,4,-[oxalylbis(trifluoromethylsulfo-nyl)imino]to[4-methylmorphilinium trifluoromethane sulfonate] (METQ) with hydrogen peroxide and a fluorophor in the presence of a, p, y, and heptakis 2,6-di-O-methyl P-cyclodextrin [66], The fluorophors studied were rhodamine B (RH B), 8-aniline-l-naphthalene sulfonic acid (ANS), potassium 2-p-toluidinylnaph-thalene-6-sulfonate (TNS), and fluorescein. It was found that TNS, ANS, and fluorescein show CL intensity enhancement in all cyclodextrins, while the CL of rhodamine B is enhanced in a- and y-cyclodextrin and reduced in P-cyclodextrin medium. The enhancement factors were found in the range of 1.4 for rhodamine B in a-cyclodextrin and 300 for TNS in heptakis 2,6-di-O-methyl P-cyclodextrin. The authors conclude that this enhancement could be attributed to increases in reaction rate, excitation efficiency, and fluorescence efficiency of the emitting species. Inclusion of a reaction intermediate and fluorophore in the cyclodextrin cavity is proposed as one possible mechanism for the observed enhancement. 

Chemiluminescence is observed from several different emitting species, depending on the analyte and reaction conditions. Vibrational overtone bands of HF in the wavelength region of =500-900 nm are observed under nearly all conditions and are often the dominant spectral feature, the (3,0), (4,0) (5,1), and (6,2) bands being the most intense, while for some reaction conditions emissions from levels up to v = 8 are observed [63], It is likely that hydrogen atoms are produced in the reaction and form vibrationally excited HF in the reaction reported by Mann et al. [62] ... 

Here, X and Y are halogens and R represents the remainder of the carbon skeleton. The reaction proceeds particularly well for the halogens chlorine and bromine, but much less so for fluorine, as the C—F bond is much stronger than either C—Cl or C—Br. However, the excited sodium halide, NaX1, is not the emitting species. Another collision between this molecule and another vapor-phase sodium atom is needed ... 

The most commonly used and widely marketed GC detector based on chemiluminescence is the FPD [82], This detector differs from other gas-phase chemiluminescence techniques described below in that it detects chemiluminescence occurring in a flame, rather than cold chemiluminescence. The high temperatures of the flame promote chemical reactions that form key reaction intermediates and may provide additional thermal excitation of the emitting species. Flame emissions may be used to selectively detect compounds containing sulfur, nitrogen, phosphorus, boron, antimony, and arsenic, and even halogens under special reaction conditions [83, 84], but commercial detectors normally are configured only for sulfur and phosphorus detection [85-87], In the FPD, the GC column extends... 

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