Chemiluminescent reaction emission spectrum

The overall reaction scheme of the luminol chemiluminescence in an aqueous medium is shown in Figure 1. The luminol oxidation leads to the formation of an aminophthalate ion in an excited state, which then emits light on return to the ground state. The quantum yield of the reaction is low ( 0.01) compared with bioluminescence reactions and the emission spectrum shows a maximum1 at 425 nm. 

DPA) in dimethylphthalate at about 70°, yields a relatively strong blue Umax =435 nm) chemiluminescence the quantum yield is about 7% that of luminol 64>. The emission spectrum matches that of DPA fluorescence so that the available excitation energy is more than 70 kcal/mole. Energy transfer was observed on other fluorescers, e.g. rubrene and fluorescein. The mechansim of the phthaloyl peroxide/fluorescer chemiluminescence reaction very probably involves radicals. Luminol also chemiluminesces when heated with phthaloyl peroxide but only in the presence of base, which suggests another mechanism. The products of phthaloyl peroxide thermolysis are carbon dioxide, benzoic acid, phthalic anhydride, o-phenyl benzoic acid and some other compounds 65>66>. It is not yet known which of them is the key intermediate which transfers its excitation energy to the fluorescer. 

Chemiluminescence is believed to arise from the 2Bj and the 2B2 electronic states, as discussed above for the reaction of NO with ozone [17]. The primary emission is in a continuum in the range =400-1400 nm, with a maximum at =615 nm at 1 torr. This emission is significantly blue-shifted with respect to chemiluminescence in the NO + 03 reaction (Xmax = 1200 nm), as shown in Figure 2, owing to the greater exothermicity available to excite the N02 product [52], At pressures above approximately 1 torr of 02, the chemiluminescence reaction becomes independent of pressure with a second-order rate coefficient of 6.4 X 10 17 cm3 molec-1 s-1. At lower pressures, however, this rate constant decreases and then levels off at a minimum of 4.2 X 1(T18 cm3 molec-1 s-1 near 1 mtorr, and the emission maximum blue shifts to =560 nm [52], These results are consistent with the above mechanism in which the fractional contribution of (N02 ) to the emission spectrum increases as the pressure is decreased, therefore decreasing the rate at which (N02 ) is deactivated to form N02. Additionally, the radiative lifetime and emission spectrum of excited-state N02 vary with pressure, as discussed above for the NO + 03 reaction [19-22],... 

The most quantitative work was done by Clyne and Thrush.89,106 In their classic studies, they passed an electric discharge through hydrogen in a flow tube, added NO past the discharge, and monitored the chemiluminescence at various points downstream. Their emission spectrum was similar to that of Clement and Ramsay,96 and they confirmed the value of 48.6 kcal/mole for D(H—NO). They further found that In (//[NO]) (/ is the emission intensity) varied linearly with reaction time (distance downstream divided by flow velocity) and with NO concentration as shown in Figures 7-1 and 7-2. Furthermore,... 

An important point is that where it has been measured, the emission spectrum produced by either a chemiluminescent reaction or by triboluminescence is the same as that found in the conventional... 

Activated chemiluminescence is observed from these secondary peroxy-esters as well. When the thermolysis of peroxyacetate [281 in benzene solution is carried out in the presence of a small amount of an easily oxidized substance the course of the reaction is changed. For example, addition of N,N-dimethyldihydrodibenzol[ac]phenazine (DMAC) to peroxyester [28] in benzene accelerates the rate of reaction and causes the generation of a modest yield of singlet excited DMAC. This is evidenced by the chemiluminescence emission spectrum which is identical to the fluorescence spectrum of DMAC obtained under similar conditions. Spectroscopic measurements indicate that the DMAC is not consumed in its reaction with peroxyester 28 even when the peroxyester is present in thirty-fold excess. The products of the reaction in the presence of DMAC remain acetophenone and acetic acid. These observations indicate that DMAC is a true catalyst for the reaction of peroxyacetate 28. The results of these experiments with DMAC, plotted according to (27) give k2 = 9.73 x 10-2 M-1 s-1. 

The Glow of Phosphorus—Effect of Pressure upon Oxidation of Phosphorus— Velocity of the Reaction—Effect of Temperature—Production of Ozone— Inhibition of the Glow—Nature of the Chemiluminescence—Ionisation by the Glow—The Emission Spectrum. 

Molecular beam experiments perhaps remain most restricted in their ability (or inability) to yield the distributions of product molecules among the various available internal energy states. Where electronically excited species are produced, the low pressure will ensure that no relaxation will occur before emission and the chemiluminescent spectrum then directly reflects the vibrational-rotational distribution produced chemically within the emitting state. Several chemiluminescent reactions have now been studied in beams, but it is not easy to estimate the ratio of the cross sections for production of excited- and ground-state product. Furthermore, collisions leading to these... 

Garvin and Greaves found that chemiluminescent radiation, in the red and infrared, was emitted during this reaction. They attributed this emission spectrum to electronically excited NO2 formed in the reaction... 

Figure 2. Visible emission spectrum from the chemiluminescent reaction of ozone with ethylene at room temperature (uncorrected for spectral sensitivity). Total pressure 0.4 torr flow rate of 0 /02 is 30 cc/min flow rate of ethylene 5 cc/min spectral slit width 10.6 nm.

Table I summarizes the primary features of the chemiluminescent emission spectra obtained from the reaction of ozone with 14 simple olefins. The observed spectra fall into three classes which correlate somewhat with the olefin structure. Class A in Table I includes the three terminal olefins studied all gave a broad, weak emission, peaking at about 440 nm. Figure 2 shows the spectrum obtained in the reaction of ozone with ethylene, a typical member of class A, at a total pressure of 0.4 torr. The emission spectrum may result from excited formaldehyde [emission...

Figure 4. Visible emission spectrum from the chemiluminescent reaction of ozone with trans-2-butene at room temperature (uncorrected for spectral sensitivity).

Class B in Table I includes seven olefins, which are characterized by dialkyl substitution at one of the carbons of the olefinic double bond. The emission spectrum produced by reaction of these olefins with ozone is characterized by a narrow band peaking at about 520 nm with broad shoulders at 465 nm and 565 nm. Figure 3 gives the chemiluminescent emission spectrum obtained by reaction of a typical member of Class B, tetramethylethylene, with ozone at a pressure of 0.8 torr. It is similar to the fluorescent emission spectrum of biacetyl [broad emission from 440-495 nm (11)1 combined with the phosphorescent emission of the same compound [narrow peaks at about 512 and 561 nm and a broad... 

The spectrum of the chemiluminescence produced by this reaction corresponded closely to the emission spectrum obtained on photoexcitation of Ru(bpy)3 [80]. 

Dessaux et al. (5, 6) observed a diffuse system of bands in the near ultraviolet which they attributed to the BClg radical. The emission spectrum was obtained as chemiluminescence in the reaction between BCl. and atomic hydrogen. They indicated that the... 

Figure 24-4 illustrates the processes involved in emission and chemiluminescence spectroscopy. Here, the analyte is stimulated by heat or electrical energy or by a chemical reaction. Emission spectroscopy usually involves methods in which the stimulus is heat or electrical energy, while chemiluminescence spectroscopy refers to excitation of the analyte by a chemical reaction. In both cases, measurement of the radiant power emitted as the analyte returns to the ground state can give information about its identity and concentration. The results of such a measurement are often expressed graphically by a spectrum, which is a plot of the emitted radiation as a function of frequency or wavelength. 

The third type of luminescence, chemiluminescence, is based on the emission of radiation by an excited species formed during a chemical reaction. In sonic instances. the excited species is the product ol a reaction belw-een the analyte and a suitable reagent (usually a strong oxidant such as ozone or hydrogen peroxide). The result is an emission spectrum characteristic of the oxidation product of the analyte or the reagent rather than the analyte itself. In other instances, the analyte is not directly involved in the chemiluminescence reaction. Instead, the analyte inhibits or has a cuialyiic effect on a chemiluminescence reaction. 

---