Known Emission Spectra

To obtain ccvrection factors, one records the onission spectrum of a standard compound and conqnres these data with the standard spectrum. By this simple conqiaradve method, one avoids the difficulties inhemit in the more tigwius iMtxedures desoibed below. Niq thol should probably not be used as a standard because, undo the conditions described, both naphthol and naphtholate emission are obsored. The dual emissicm is a result of an ited-state ration, the extmt of which is difficult to control. The use of quinine sulf as a standard has been 

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Programming a CAM for fluorometry is far more complex than for spectrophotometry. Spectrophotometry is simple because it is based on the ratio of light in to light out. But fluorometry creates many of the problems associated with true radiometry—measuring the emission spectrum of an unknown source. The logic may become circular. Radiometry to determine an emission spectrum requires the relative spectral sensitivity of the photometer to be known, but how can this be determined without a source with a known emission spectrum Fortunately, physicists in our national standardization organizations provide us with calibrated sources and photometers. 

A rigorous means for removing discontinuities between segments is the use of luminescent standards described in Section 10.3. The standard has a known emission spectrum, which is recorded with the same set of segments as the Raman spectrum of interest (34). The standard emission experiences the same response variations as the Raman scattering, so its spectrum includes the same... 

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. 

Proper correction of the emission spectrum is a prerequisite for the measurement of the fluorescence quantum yield of a compound. Quantum yields are usually determined by comparison with a fluorescence standard4, i.e. a compound of known quantum yield that would ideally satisfy the following criteria (Demas, 1982) ... 

A study of the wavelength or frequency of radiation absorbed or emitted by an atom or a molecule will give information about its identity and this technique is known as qualitative spectroscopy. This information is usually reported as the wavelength of radiation involved and is most easily represented as an absorption or emission spectrum (Figure 2.2). Measurement of the total amount of radiation will give information about the number of absorbing or emitting atoms or molecules and is called quantitative spectroscopy. 

In the ideal case of free Eu + ions, we first must observe that the components of the electric dipole moment, e x, y, z), belong to the irreducible representation in the full rotation group. This can be seen, for instance, from the character table of group 0 (Table 7.4), where the dipole moment operator transforms as the T representation, which corresponds to in the full rotation group (Table 7.5). Since Z)° x Z) = Z) only the Dq -> Fi transition would be allowed at electric dipole order. This is, of course, the well known selection rule A.I = 0, 1 (except for / = 0 / = 0) from quantum mechanics. Thus, the emission spectrum of free Eu + ions would consist of a single Dq Ei transition, as indicated by an arrow in Figure 7.7 and sketched in Figure 7.8. 

This phenomenon is known as the inverse Raman effect and was first observed by Stoicheff The inverse Raman spectrum is the analogue of the stimulated Raman emission spectrum and therefore theories of the stimulated Raman effect apply to both emission and absorption. There are, however, significant differences in the corresponding spectra ... 

Luminescence of in synthetic alkaline earth sulfates is well known (Folk-erts et al. 1995). In this study, CaS04 Pb shows an emission band with a maximum at 235 nm at 300 K, while the excitation maximum is at 220 nm. The decay curve of the emission is single exponential with a decay time of 570 ps at 4.2 K. The emission spectrum of BaS04 Pb demonstrates a broad band peaking at 340 nm with an excitation maximum at 220 nm, while in SrS04 Pb the luminescence band has a maximum at 380 nm. hi natural barite and anhydrite samples we detected several narrow UV bands, which may be connected with Pb emission, but for confident conclusion additional study is needed. In any case, Pb participation in natural sulfates liuninescence has to be taken into consideration. 

In the emission spectrum analysis, a small piece of material to be analyzed is heated (burned) in an electric arc or spark and its spectrum recorded by means of a spectrometer. By comparing the wave lengths of the spectrum with.chose produced by known materials, it is possible to determine rapidly the composition of the sample... 

The insulating action of the —CH2— group between the phenyl ring and the amino radical in benzylamine can be inferred from another group of experiments. It is well known that under vacuum u.v. irradiation of NH3 and the aliphatic amines the emission spectrum of the excited NH2 radical (a-band system) has been observed.26 Attempts in this laboratory to produce the same luminescent photodissociation in aniline vapor have so far failed. On the other hand, in benzylamine vapor the bands of the -NHj radical are easily observed on illumination by light in the vacuum u.v. range.31... 

In the same way, the sodium atoms can be promoted to the doublet levels 3 2Py2 or 3 2Ptii which are split due to spin-orbit coupling. When such atoms return to the ground state, the two closely spaced lines are observed in the emission spectrum. These are the well known D lines of sodium (Figure 2.5). 

For recording of the emission spectrum, the emitted radiation is focussed on the slit of a monochromator and intensities measured attach wavelength. Since sensitivities of photocells or photomultipliers are wavelength dependent, a standardization of the detector-monochromator combination is necessary for obtaining true emission spectrum This can be done by using a standard lamp of known colour temperature whose emission characteristics is obtained from Planck s radiation law. The correction term is applied to the instrumental readings at each wavelength. Very often substances whose emission spectra have been accurately determined in the units of relative quanta per unit wavenumber intervals are... 

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