Absorption temperature effects

Ozin, Hanlan, and Power, using optical spectroscopy (49,121). In view of the marked temperature-effect observed for the cobalt system, we shall focus on this cluster system here. Evidence for cobalt-atom aggregation at the few-atom extreme first came from a comparison of the optical data for Co Ar — 1 10 mixtures recorded at 4.2 and 12 K (see Fig. 4). A differential of roughly 8 K in this cryogenic-temperature regime was sufficient to cause the dramatic appearance of an entirely new set of optical absorptions in the regions 320-340 and 270-280 nm (see Fig. 4). Matrix variation, from Ar, to Kr, to Xe, helped clarify atom-cluster, band-overlap problems (see Fig. 5). 

The temperature effect on the absorption spectra is also shown in Fig. 2. One can see that the peak position and bandwidth of the P band increase with temperature, while in other bands (like the B and H bands) only its bandwidths show a positive temperature effect. It is important to note that even though the RC is a complicated system, its spectra are relatively simple and its bandwidth is not particularly broad. The above features of absorption spectra of RCs need to be taken into account when analyzing the observed absorption spectra. 

There is a potentially important influence of ice and snow at the surface, for ice and snow have high albedos. Ice-albedo feedback may increase the sensitivity of the climate system. That is, low temperature causes more ice and a higher albedo, allowing less absorption of sunlight and therefore causing a still lower temperature. This temperature effect is included by... 

It is important to note that the calculation of the initial concentrations of phenol ( 10-2 mol dm-3) and acetonitrile (possibly 1 mol dm-3) were corrected for the density of the solvent at each temperature. The temperature effect on the molar absorption coefficient (e) was also considered when relating [PhOH] to the absorbance of the O-H free band. This was empirically made by measuring the absorbances (A) of a phenol solution (in the same solvent and with a concentration similar to that used in the equilibrium study) over the experimental temperature range. For each temperature, the Lambert-Beer law [312],... 

Finally, although temperature had a large effect on both the position (wavelength) and the intensity of the water absorption bands in the emulsion NIR spectra, careful experimentation demonstrated that the 1618 nm vinyl C—H band used in the calibration model did not shift in either position or intensity with temperature, in the temperature range used in these studies (25-75° C). Therefore, it was not necessary to correct the calibration model for temperature effects, either by the use of internal or external standards, or by including temperature variations in the calibration set. 

For both AP-CVD and LP-CVD processes, the main observation concerning the variation of the transparency of the ZnO films is a reduction of transmittance in the near-infrared (N1R) range when the substrate temperature is increased. Indeed, N is usually increased with temperature, and this leads to a stronger free carrier absorption (FCA) effect for higher substrate temperatures. 

It is obvious from the reported studies that temperature effects are not very important in the majority of gas-liquid reaction systems. For a few systems, where large amounts of heat may be liberated, the compensating effects such as the ones mentioned above would decrease its effect on the rate of absorption. 

In infrared spectra, absorption is almost always plotted against frequency (or wavelength). Often, absorption of acoustical waves (E or tan S) is plotted against acoustical frequency. Equally often, measurements of mechanical behavior are made as a function of temperature. This is because temperature effects are usually more marked in polymer transitions than in infrared spectra. However, infrared absorption at a single frequency does vary with temperature in a manner somewhat analogous to the mechanical studies. 

Fig. 19. Temperature effects on the dimer (2-2) absorption spectrum At —113 °C, almost pure dimer is present. At —60 °C, the maximum is at 345 nm. Further temperature increases (up to —8 °C) shift the maximum gradually to 340 nm, and decrease the intensity, the final spectrum being taken after recooling to 77 K...

Kirmaier, C., and Holten, D., 1988, Temperature effects on the ground state absorption spectra and electron transfer kinetics of bacterial reaction centers. In NATO ASI Ser., Ser. A, 149 219n228. 

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