Temperature-dependent absorption spectra

As mentioned in the previous section, the temperature-dependent absorption spectra of RCs are very important for the understanding of the molecular properties such as the electronic configurations, vibrational contributions, and transition moment relations of the Bchls in RCs. However, only in the R26. Phe-a mutant case have absorption spectra at various temperatures so far been available. Although the absorption spectra of the WT and R26 mutant RCs are available at a few temperatures like IK, 4K, 77K, and 298K, the analyzed results are not so consistent (see Table III). It may be because the preparation... 

Mostafavi M, Lin M, He H, Muroya Y, Katsumura Y. (2004) Temperature-dependent absorption spectra of the solvated electron in ethylene glycol at 100 atm studied by pulse radiolysis from 296 to 598 K. Chem Phys Lett 384 52-55. 

We have emphasized the importance of the low frequency (-100 cm-i) special pair intermolecular mode of coupling strength, 0 = 100 cm-i (Huang-Rhys factor S = 1). The temperature dependent absorption spectra of Shuvalov et al. reported later show an evidence of the special pair mode of 140 cm- (S = 1.2) [13]. A recent holebuming experiment of Small and coworkers reveals several distinctive structures in the hole spectra of the special pair. The Y-hole can be attributed as a vibronic progression hole of -120 cm-i of the X-hole situated near the spectral 0-0 line [14]. 

However, the fact that the time-evolution ofthe absorption spectrum ofthe solvated electron can be accurately described by the temperature-dependent absorption spectrum ofthe ground state solvated electron (Fig. 11) suggests that the spectral blue shift would be mostly caused by a continuous relaxation, or"cooling"of the electron trapped in a solvent cavity.To conclude, this analysis clearly indicates that it is not obvious to select a unique model to describe the solvation dynamics of electron in ethane-1,2-diol, and in other solvents. 

Unlike the triplet contributions to the absorption spectrum, the singlet contributions have a strongly temperature-dependent absorption coefficent k. A fit between the experimental spectrum of Figure 4 and calculated spectra as in Figure 3 yields T = 1900 ( 200) K for the -X 2g maximum and T = 2700 ( 200) K for the A 2 <- X 2g satellite. The difference can be explained by the different temperature dependenees of k in conjunction with the radial temperature profile of the discharge. 

W.S. Pegau, J.R.V. Zaneveld (1993). Temperature-dependent absorption of water in the red and near-infrared portions of the spectrum. Limnol. Oceanogr., 38,188-192. 

As we proposed elsewhere (2), low-temperature induced shifts in the light absorption spectrum of the intact Anacystis cells can be used to detect the phase-transition of the cytoplasmic membrane in vivo. The temperature-dependent absorption change (A q in intact, CP-treated cells is shown on Fig.2. 

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. 

---