Spontaneous spectrum

Only those Raman lines which are most intense in the spontaneous spectrum show up in the stimulated spectrum (these are commonly one or two lines). 

Pulsed laser-Raman spectroscopy is an attractive candidate for chemical diagnostics of reactions of explosives which take place on a sub-microsecond time scale. Inverse Raman (IRS) or stimulated Raman loss (.1, ) and Raman Induced Kerr Effect (2) Spectroscopies (RIKES) are particularly attractive for singlepulse work on such reactions in condensed phases for the following reasons (1) simplicity of operation, only beam overlap is required (2) no non-resonant interference with the spontaneous spectrum (3) for IRS and some variations of RIKES, the intensity is linear in concentration, pump power, and cross-secti on. 

Fig. 17. a) Gain and b) Spontaneous spectrum as a function of electron energy. I(t) indicates the fall-off of Synchrotron Radiation intensity as the electron energy is lowered during the experiment. 

The above fomuilae for the absorption spectrum can be applied, with minor modifications, to other one-photon spectroscopies, for example, emission spectroscopy, photoionization spectroscopy and photodetachment spectroscopy (photoionization of a negative ion). For stimulated emission spectroscopy, the factor of fflj is simply replaced by cOg, the stimulated light frequency however, for spontaneous emission... 

The interpretation of emission spectra is somewhat different but similar to that of absorption spectra. The intensity observed m a typical emission spectrum is a complicated fiinction of the excitation conditions which detennine the number of excited states produced, quenching processes which compete with emission, and the efficiency of the detection system. The quantities of theoretical interest which replace the integrated intensity of absorption spectroscopy are the rate constant for spontaneous emission and the related excited-state lifetime. 

Gr. technetos, artificial) Element 43 was predicted on the basis of the periodic table, and was erroneously reported as having been discovered in 1925, at which time it was named masurium. The element was actually discovered by Perrier and Segre in Italy in 1937. It was found in a sample of molybdenum, which was bombarded by deuterons in the Berkeley cyclotron, and which E. Eawrence sent to these investigators. Technetium was the first element to be produced artificially. Since its discovery, searches for the element in terrestrial material have been made. Finally in 1962, technetium-99 was isolated and identified in African pitchblende (a uranium rich ore) in extremely minute quantities as a spontaneous fission product of uranium-238 by B.T. Kenna and P.K. Kuroda. If it does exist, the concentration must be very small. Technetium has been found in the spectrum of S-, M-, and N-type stars, and its presence in stellar matter is leading to new theories of the production of heavy elements in the stars. 

The variety of fluoride compounds that exist and the wide spectrum of their preparation methods are related to the properties of fluorine, and above all to fluorine s high electronegativity. Low dissociation energy of the fluorine molecule, F2, relatively high energies of bond formation found in most fluoride compounds, as well as fluorine s strong oxidizing ability lead, in some cases, to spontaneous fluorination. 

In the previous section we have shown that for an excitation density above the PL line-narrowing threshold, the shape of the SE spectrum remain unchanged. This demonstrates that the spontaneous emission spike is not due to a new transition existing in the phoioexcited material, as would be the case for excitonic mol-... 

Thus, the 2-methyl derivative of the imidazopyrazinone (above) dissolved in DMSO spontaneously emits blue light (A.max 450 nm) in the presence of air (Goto, 1968), like the 2-benzyl derivative (Amax 475 nm), the 2-methyl-6(p-hydroxyphenyl) derivative (MCLA 7max 468 nm), and coelenterazine (Amax 465 nm) under similar conditions (Fig. 5.3). The comparison of the luminescence spectra of these compounds shows that the 6-position substituent has little influence on the luminescence spectrum of coelenterazine derivatives, despite the apparent conjugation between the 6-phenyl ring and the imidazopyrazinone ring in the structures of MCLA and coelenterazine. 

Odontosyllis luciferin is colorless and shows an absorption maximum at about 330 nm in aqueous ethanol (Figs. 7.2.1 and 7.2.2), and it undergoes various spectrum changes upon spontaneous oxidation... 

From CS2 solution S7O2 is obtained as intensely orange colored crystals which on heating spontaneously decompose at 60-62 °C with evolution of sulfur dioxide. S7O2 is far less soluble in CS2 (ca. 1 g at 0 °C) than S7O. The solution decomposes within 1 h to a mixture of sulfur homocycles and SO2. Solid S7O2 decomposes at 25 °C within minutes and quantitatively within 2 h, even in the dark. Heating in a high vacuum to 50-60 °C produces S2O and elemental sulfur. The El mass spectrum therefore exhibits peaks due to these decomposition products only [67]. 

The wavenumbers of the observed bands are identical with those of the spontaneous Raman spectrum of the solution and oxazine solid [27]. The impulsive stimulated Raman transition may initiate coherent vibrations in the electronic excited state. However, there was no sign of the excited-state vibrations superimposed on the ground-state bands in the spectrum of Figure 6.3. 

The emission spectmm of Co, as recorded with an ideal detector with energy-independent efficiency and constant resolution (line width), is shown in Fig. 3.6b. In addition to the expected three y-lines of Fe at 14.4, 122, and 136 keV, there is also a strong X-ray line at 6.4 keV. This is due to an after-effect of K-capture, arising from electron-hole recombination in the K-shell of the atom. The spontaneous transition of an L-electron filling up the hole in the K-shell yields Fe-X X-radiation. However, in a practical Mossbauer experiment, this and other soft X-rays rarely reach the y-detector because of the strong mass absorption in the Mossbauer sample. On the other hand, the sample itself may also emit substantial X-ray fluorescence (XRF) radiation, resulting from photo absorption of y-rays (not shown here). Another X-ray line is expected to appear in the y-spectrum due to XRF of the carrier material of the source. For rhodium metal, which is commonly used as the source matrix for Co, the corresponding line is found at 22 keV. 

ESR spectrum of the RjSn radical (R = 2,4,6-triisopropylphenyl), spontaneously generated upon dissolving distannane RBSn-SnRj in deoxygenated toluene, revealed at -140°C in the solid state the Sn hfcc of 163 Such a radical is more planar than the PhjSn radical ( Sn hfcc = 186.6mT) but less planar than the MejSn radical C Snhfcc = 161.1 mT)3° ... 

Sanders (14) has exploited the strong and selective coordination of phosphine donor groups to Ru(II) to construct hetero-dimetallic porphyrin dimers (17, Fig. 5). An alkyne-phosphine moiety introduced on the periphery of a free base or metalloporphyrin (M = Zn or Ni) spontaneously coordinates to a Ru(II)(CO) porphyrin when the two porphyrins are mixed in a 1 1 ratio. Coordination is characterized by a downfield shift of the 31P resonance (A<531P = 19 ppm). There is no evidence of self-coordination of the zinc porphyrin at 10 6 m in toluene, there is no shift in the Soret band in the UV-Vis absorption spectrum. The Ni-Ru dimer was observed by MALDI-TOF mass spectrometry. Heating the Ru(II)CO porphyrin with 2 equivalents of the phosphine porphyrins led to quantitative formation of trimeric assemblies. 

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