Temperature-Dependent Measurements

Final state Calculated yield Observed yield 

Subsequent to the initial 300 K observations, measurements were done as a function of temperature. The first measurements, by Koch era/.,18 were done at 

Experiments with Xe analogous to the previously described Xe experiment were carried out at both 90 K and 300 K. Specifically the time dependences of the populations in higher nd and ng states were measured subsequent to population of an nf state by a pulsed laser.19 The time dependences of the observed populations were fit to a model which yielded the radiative transfer rates from the initially excited state to the final states. Not surprisingly, as the temperature was reduced from 300 K to 90 K, not only was the overall radiative transfer reduced, but the transfer to the highest lying states was most sharply reduced, as expected from the dependence of the photon occupation number on frequency and temperature. For example the transfer from the Xe 25f to 26d,g states was reduced by a factor of 3 while the 25f-27d,g transfer was reduced by a factor closer to 5. 

Spencer et al. populated the Na 19s state and observed the sum of the populations in the 19s, 19p, and 18p states, at times from 2-32 /is after the laser excitation, to determine the sum of the radiative transition rates from the 19s to 18p and 19p states.20 The measurements were made at temperatures from 6 K to 210 K with the results shown in Fig. 5.6. As shown by Fig. 5.6, the observed rates agree well with the calculated rates, shown by the line. At 0 K the rate is entirely due to the spontaneous 19s — 18p transition, and the increase above this rate is due to thermal radiative transfer to both the 18p and 19p states. It is interesting to note that above 30 K the transfer rate increases linearly with T as expected from Eq. (5.16). The linear behavior only occurs above 30 K since only then is kT (o for these two transitions. 

While the Na 19s — 18p, 19p transfer rate is an excellent illustration of the validity of Eq. (5.16) for co kT, the photoionization of Rydberg atoms of n = 20 by black body radiation is a test of the regime a kT, and this regime has been explored by Spencer et al 21 Specifically, they measured the relative rates for 

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Following the general trend of looldng for a molecular description of the properties of matter, self-diffusion in liquids has become a key quantity for interpretation and modeling of transport in liquids [5]. Self-diffusion coefficients can be combined with other data, such as viscosities, electrical conductivities, densities, etc., in order to evaluate and improve solvodynamic models such as the Stokes-Einstein type [6-9]. From temperature-dependent measurements, activation energies can be calculated by the Arrhenius or the Vogel-Tamman-Fulcher equation (VTF), in order to evaluate models that treat the diffusion process similarly to diffusion in the solid state with jump or hole models [1, 2, 7]. 

An important accessory in many applications of Mossbauer spectroscopy is a cryostat for low temperature and temperature-dependent measurements. This may be necessary to keep samples frozen or to overcome small Debye-Waller factors of the absorbers at room temperature in the case of an isotope with high y-energy. Paramagnetic samples are measured at liquid-helium temperatures to slow down... 

Studies like those mentioned here on the osmium complexes are more difficult for related complexes of ruthenium because of the intervention of a lowlying, thermally populable d-d excited state. However, it is possible to separate the two contributions to excited state decay by temperature dependent measurements. In the case of Ru(bpy>32+, temperature dependent lifetime studies have been carried out in a series of solvent, and the results obtained for the variation of knr with Eem are in agreement with those obtained for the Os complexes (19). 

Fig. A2.2. Temperature dependences measured for the haliwidths Av n of the IR absorption bands for valence vibrations of OH(D) groups on Si02 surface (filled markers) and recalculated for the halfwidths w of three components of Lorentzian lines (empty markers) for OH (1) and (OD) groups of high concentration (2), and for (OD) groups of low concentration (3).2"2...

For polyethylene (PE) and PEP systematic temperature-dependent measurements in the Rouse regime were performed. Furthermore data on the temperature-dependent end-to-end chain distance (Rl) also exist. Table 3.2 displays... 

Informations on the vibrational and electron mean free path properties. Such analysis is possible only if the interface phase is very well defined, and if temperature dependent measurements are done and compared. Debye Waller effects can be tangled with ordering transformation of the interface phase as a function of temperature and so on. If a single phase interface with order at least to the second nearest neighbour is recognised, then a temperature dependent Debye Waller, and mean free path analysis can be attempted. 

These lines are also drawn in Fig. 1. It is clear that the agreement is quite nice. Similar fitting equations in heavy water for CANDU reactors were also obtained [19]. Furthermore, temperature-dependence measurements with fast neutrons and high LET ion beams were also investigated [20,23]. 

Three factors support the contention that the rheological properties -n and t may not be correct (a) no temperature dependency measurements are available and the room-temperature data cannot possibly apply rigorously (b) with the more dilute suspensions, Bonilla et al. (B6) encountered serious settling problems in the Mac Michael viscometer used to measure these properties (c) for all suspensions the reported values of r are surprisingly low. 

Such a design combines the bubble-cell characteristics, together with an U-type design of the glass tube employed as the NMR detector. The glass tube is positioned within a glass Dewar, thus enabling temperature-dependent measurements. Another feature is the direct attachment of the NMR radiofrequency... 

The present work summarizes opportunities of using high-resolution synchrotron and standard xrd techniques for structural characterization as well as for investigations of structure-property-relationships. xrd will be used to determine quantitatively the phase content of morphotropic pzt. Temperature dependent measurements provide information about the phase transformation of morphotropic donor doped pzt ceramics and high-resolution synchrotron X-ray diffraction gives information about the extrinsic and intrinsic contributions to the electric field induced strain, xrd results are finally compared with electrical measurements to analyze the interactions among microstructure, phase content and properties. 

Materials at temperatures above the glass transition temperature (Tg) absorb Xe readily, therefore the fact that after sealing of the sample tube the density of the Xe gas could decrease with time when more Xe is absorbed by the material is neglected. For samples which absorb Xe slowly, like some polymers below their T, this effect may not be negligible. Also for temperature dependent measurements the variation of the coefficients in Equation 12.1 with temperature should be taken into account [4, 5, 6], but in view of the widths of the resonance lines investigated here as a function of temperature, the temperature dependence of the reference has also been neglected. 

It must be remembered, furthermore, that the identification of the H-atom translocation mode is not equivalent to the identification of the reaction coordinate. We have attributed the absence of a deuterium isotope effect on the excited-state H-atom transfer (for the 10-ps component in hypericin and hypo-crellin A) to the zero-point energy in the proton coordinate lying above the barrier, with the H-atom being effectively delocalized between the two oxygen atoms. Consequently, the reaction coordinate for the excited-state H-atom transfer cannot be identified with the proton coordinate, and it must be concluded that other intramolecular motions are in fact responsible for the process. Temperature-dependent measurements indicate that these motions are extremely low amplitude, Ea 0.05 kcal/mol for hypericin [37]. Because the nature of this motion is not yet identified, we refer to it as the skeleton coordinate [48, 71, 82]. We propose that it is the time scale for this latter conformational change... 

Temperature-dependent measurements of Ti have also been performed for the 33S in the thiosulphur position of the SyO anion (as a function of concentration and temperature),80 as well as for sulpholane 10, butadiene sulphone 11 and dimethyl sulphone (in DMSO-d6 and CDC13).75... 

Ignoring the effect of the proximity of steps, for both systems it was found that the jump length distribution is independent of temperature over the temperature interval from 304 to 342 K. Temperature dependent measurements of the rate of long jumps of the In and Pd atoms were performed over the same temperature interval. The results for both systems are plotted in Fig. 12. 

The resulting estimates of <5r/c i for Cr(III)/Cr(II) aquo couples, ca. 0.1-0.3 A, are close to that extracted from temperature-dependence measurements and indicate that these strongly hydrated species follow marginally non-adiab-atic pathways even at the plane of closest approach [30]. Markedly larger values of 5rK°eU ca. 5 A, were obtained for similar ammine complexes, as from a related comparison involving unimolecular outer-sphere reactivities [21], This is consistent with the smaller hydrated radii of the ammines allowing a closer approach to the metal surface, whereupon a 1 [15a, 30]. 

High-resolution and temperature-dependence measurements were recorded for the lowest-energy UV transition (230-250 nm) of thiophene. Based on these results, the first system of the UV spectmm is assigned to the tp4<—tpT, (B2) transition <1982J(P2)761>. 

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