Broadening of emission

For free atoms, or atoms in molecules, these recoil effects are typically about five to six orders of magnitude larger than the natural line width, and so there is no possibility of a resonance phenomenon (but having said that, under very special conditions resonances for gases have in fact been achieved). Even in the liquid state, atom or molecule movements are generally too large. However, when both emitter and absorber atoms are bound in solid samples recoilless nuclear resonance absorption becomes observable. But even here the atomic movements due to lattice and molecular vibrations lead to broadening of emission and absorption lines. We must therefore expect temperature-dependent effects in Mossbauer spectroscopy. 

Palladium clusters deposited on amorphous carbon have been studied by XPS and UPS [28] and both techniques show broadening of the d-band peak as cluster size increases. The d-threshold shifts towards Ep as cluster size increases. In UPS studies the d-emission of the single atom has its peak at 3.0 eV below Ep, whereas the d-threshold is 2eV below Ep. Palladium clusters evaporated onto Si02 have been studied by UPS [38]. At large coverages of the Pd metal evaporated (> 10 atoms/cm ), a high emission intensity at Ep excited with photons of 21.2 eV (He(I)) or 40.8 eV (He(II)) as excitation source, is observed. This feature is characteristic in the spectra from bulk Pd samples. At the lowest metal coverage (3 x 10 atoms/cm ),... 

Initial position of instant spectrum of fluorescence and character of spectral shifts in time depend on the excitation frequency, i.e., inhomogeneous broadening is of dynamic nature as a degree of broadening is maximal at the initial instants of time and decreases with time of emission registration (demonstration in panel d of Fig. 5). 

The ratio of the intensity of anti-Stokes and Stokes lines is primarily determined by the Boltzmann population of the excited vibrational states. For mid-IR frequencies this fractional population is very low (seIO-4 at 2000cm-1). As a result, Raman spectra are usually taken from the Stokes side of the Rayleigh line as these are generally very much more intense and are not broadened by emissions from hot states. 

For the distyrylbenzene carbon-centered tetramer 46b, the fluorescence spectrum in the solid him differs from the spectra in solution or in a polymer matrix due to excimer formation [93]. A concentration of 5% in a polystyrene matrix is sufficient for a distinct broadening of the emission. For the higher homologue 46c, a fluorescence maximum of 472 nm was measured in freshly prepared films. If the film is thermally annealed, the spectrum shifts to 511 nm, probably due to intermolecular arrangement that favors excimer formation. 

It is worthwhile to recognize that if the mechanism of the Auer mantle is indeed the theorem of Kirchhoff (opaque standard behaviour in the absorption bands strongly reduced emission outside the absorption bands) the principle of Franck and Condon applies to the thermal emission determined by the distribution of nuclear positions in the (hot) groundstates. In particular, one would not expect the slightest broadening of the emission bands relative to the absorption bands at the same T. The fluorescent or chemo-luminescent behaviour is entirely different in this respect. 

Experimental details for the cross-section measurements were presented in the literature. Briefly, after the irradiation by electron beam pulse for a few nanoseconds, the time-dependent absorption for the atomic line transition Rg Rg -i-/zv was measured to observe the time-dependent population of the excited rare gas atoms Rg. The population of excited Rg was determined using an absorption law for the atomic lines, where the broadening of the absorption profile due to the thermal Doppler effect and due to the attractive interatomic potentials was reasonably taken into consideration. The time-dependent optical emission from energy transfer products, such as ... 

Describe the factors which cause broadening of spectral lines. In atomic absorption spectrometry, why is it preferable for the source line-width to be narrower than the absorption profile How can this be achieved What are the differing requirements for resolution in monochromators for atomic emission and for atomic absorption spectrometry ... 

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