Temperature dependence absorption spectra

The profile of the absorption spectrum will depend extensively on the relative position of the value of Ei which depends on the different vibrational states. The intensity of absorption spectrum will depend, among others, on the population of molecules reaching the excited state. More this population is important, more the intensity of the corresponding absorption spectrum is high. Therefore, recording an absorption spectrum of the same molecule at different temperatures should in principle yield altered or modified absorption spectra. 

The bleaching of rhodopsin has been found to lead to the all-trans form of retinal through several intermediate steps.(llb,45) These steps are temperature dependent consequently low temperatures must be used to observe the intermediate products. A solution of rhodopsin is subjected to a flash of light at liquid nitrogen temperature and intermediates are detected by changes in the absorption spectrum. The first intermediate, with an absorption maximum at 543 nm, believed to be an all-fra/w-retinal bound to opsin, has been termed prelumirhodopsin. Warming the sample to a temperature greater than... 

Figure 15. Temperature dependence of absorption spectrum of the viologen bilayer membrane having biphenyl chromophore, CnBphCfV 2Br in water.

Thus making samples not too thick helps in getting sharper spectra and facilitates the quantitative interpretation. Finally, particularly in the Mossbauer spectra of small catalyst particles, one should be aware of the temperature dependence of the absorption area through the recoil-free fraction. If the spectrum contains contributions from surface and bulk phases, the intensity of the former will be greatly underestimated if the spectrum is measured at room temperature. The only way to obtain reliable concentrations of surface and bulk phases is to determine their spectral contributions as a function of temperature and make an extrapolation to zero Kelvin [13]. 

Figure 2.11. The dependence of the position of the fluorescence spectrum maximum on excitation wavelength for tryptophan in a model medium (glycerol) at different temperatures (a) and singletryptophan proteins (b). 1, Whiting parvalbumin, pH 6.S in the presence of Ca2+ ions 2, ribonuclease Th pH 6.5 3, ribonuclease C2, pH 6.5 4, human serum albumin, pH 7.0, +10"4 M sodium dodecyl sulfate 5, human serum albumin, pH 3.2 6, melittin, pH 7.5, +0.15 M NaCl 7, protease inhibitor IT-AJ from Actinomyces janthinus, pH 2.9 8, human serum albumin, pH 7.0 9, -casein, pH 7.5 10, protease inhibitor IT-AJ, pH 7.0 11, basic myelin protein, pH 7.0 12, melittin in water. The dashed line is the absorption spectrum of tryptophan.

Figure 4.10(b) shows the temperature dependence of the absorption spectrum expected for an indirect gap. It can be noted that the contribution due to becomes less important with decreasing temperature. This is due to the temperature dependence of the phonon density factor (see Equation (4.37)). Indeed, at 0 K there are no phonons to be absorbed and only one straight line, related to a phonon emission process, is observed. From Figure 4.10(b) we can also infer that cog shifts to higher values as the temperature decreases, which reflects the temperature dependence of the energy... 

Electrons in nonpolar liquids are either in the conduction band, trapped in a cavity in the liquid, or in special cases form solvent anions. The energy of the bottom of the conduction band is termed Vq. Vq has been measured for many liquids and its dependence on temperature and pressure has also been measured. New techniques have provided quite accurate values of Vq for the liquid rare gases. The energies of the trapped state have also been derived for several liquids from studies of equilibrium electron reactions. A characteristic of the trapped electron is its broad absorption spectrum in the infrared. 

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