Low temperature measurements

Using the refinement parameters, electron density maps were calculated. Figure 1 shows an example derived from CU96. According to all refinement results the intensities of the strong reflections were too low. Therefore, they were omitted for the electron density studies. The problem is currently under study. Additionally, low-temperature measurements are planned for the near future. 

The model proposed by Anderson and Phillips gives a phenomenological explanation of the properties of the amorphous materials without supplying a detailed microscopic description [42]. Low-temperature measurements of the specific heat of amorphous solids have however shown that instead of a linear contribution as expected from the TLS theory, the best representation of data is obtained with an overlinear term of the type [43,44] ... 

In a classical low-temperature measurement of heat capacity, the sample is placed (usually glued) onto a low heat capacity support which is thermally linked to the thermal bath by a thermal conductance (see Fig. 12.1). 

Seven simulations were carried out at temperatures ranging between 7 and 16 mK. Data used at the various temperatures for the lumped elements are plausible values estimated from very low-temperature measurements. They are reported in Table 15.2. 

In the case of the sulphur triimide S(NBu-f)3, the dispersive Raman technique applying a double monochromator and a CCD camera was employed to obtain the information from polarized measurements (solution studies) and also to obtain high-resolution spectra by low-temperature measurements. In the case of the main group metal complex, only FT-Raman studies with long-wavenumber excitation were successful, since visible-light excitation caused strong fluorescence. The FT-Raman spectra of the tetraimidosulphate residue were similar to those obtained from excitation with visible laser lines. 

The amount of oxygen adsorbed in a monolayer on 1 g of a sample of silica gel at low temperature, measured as the volume of oxygen adsorbed, was 105 cill at 300 K and 1 atm. If the cross-sectional area for oxygen is taken as 14 A, determine the surface area per gram for this silica sample. 

Papavassihou GC, Mousdis GA, Zamhounis IS, Terzis A, Hountas A, Hilti B, Mayer CW, Pfeiffer J (1988) Low temperature measurements of the electrical conductivities of some charge transfer salts with the asymmetric donors MDT-TTF, EDT-TTF and EDT-DSDTF. (MDT-TTF)2Aul2, a new superconductor (T = 3.5 K at ambient pressure). Synth Met B27 379-383... 

Harwood, M. H and R. L. Jones, Temperature Dependent Ultraviolet-Visible Absorption Cross Sections of N02 and N204 Low-Temperature Measurements of the Equilibrium Constant for 2N02 N204, J. Geophys. Res., 99, 22955-22964 (1994). 

Multiple-pulse measurements were performed on both the LP and HP samples at 20° and — 80° C, and when no differences were noted, lower temperature measurements were performed only on the LP sample. Multiple-pulse spectra for the LP sample are illustrated in Figure 4 together with the eight-pulse spectrum of the reference used for the low-temperature measurements, Ca(OH)2. The lineshapes observed are quite broad, and the line center is a function of temperature. The line width was separated into three contributions by performing three related multiple-pulse measurements (I). These indicated that the main contributions to the linewidth came from both relaxation and second-order dipolar effects. The maximum possible field inhomogeneity Hamiltonian is estimated to be less than 16 ppm by this means, which indicates that the com-... 

Spectra like the ones shown in Fig. 3.10 may be readily decomposed into their line profiles. As an example, we show that the low-temperature measurement may be accurately represented by three identical profiles. Using the so-called BC model profile with three adjustable parameters and centering one at zero frequency (the Qo(l) line), another one at 354 cm-1 (the H2 So(0) line) and the third one at 587 cm-1 (the So(l) line), one may fit the measurement using least mean squares techniques, Fig. 3.11. The superposition (heavy line type) of the three profiles (thin... 

Figures 3.46 (p. 126) and 6.2 show the measured three-body moments (squares, dots, etc.) as function of temperature. A visual average of the data presented is sketched (thin line). For comparison, the calculated theoretical predictions are also plotted (heavy curves). Both the measured and computed moments yn increase with increasing temperature. However, the measurements increase faster with temperature than the calculations. Moments are negative at low temperature measured moments turn positive at some intermediate temperature. Theory and measurements never coincide, the measured values always being greater if T > 50 K.

In the second part, examples of electrochemical studies at low temperatures will be given, followed by a discussion of some of the practical aspects of doing electrochemistry under such conditions. Some of the techniques and procedures differ considerably from those of high-temperature electrochemistry, and, in fact, this field of low-temperature measurements has been given the moniker cryo-electrochemistry. 

It is much more popular to use nonaqueous solvents for low-temperature studies. There are two motivations, the more common of which is the desire to make measurements down to the lowest temperature possible using a solvent/ electrolyte system compatible with the chemical properties of the substances to be studied. In other instances, the purpose of the experiments is to study the effect of solvent on a temperature-sensitive parameter (e.g., a heterogeneous electron-transfer rate constant [5]), so a variety of solvents is sought in which low-temperature measurements can be made. 

It would be valuable to fill some of the di-rr/di-cr gaps in Table VII. It would also be of interest to extend the data from -complex and ethylidyne species on the missing metals Fe and Os, and from n complexes alone for Co and Ru. Low-temperature measurements are likely to be particularly fruitful so that some spectra could be obtained without overlap from ethylidyne features. 

The resulting principal values of the 13C chemical shift tensors of the C60 carbons are 8n = 228 ppm, 822 = 178 ppm, and 833 = -3 ppm. Tycko et al reportet the experimental values 8n = 213 ppm, S22 = 182 ppm, and 833 = 33 ppm obtained from low temperature measurements of a powder pattern spectrum (18). However, the spectra have a low signal to noise ratio and a wide slope so that a larger error for the experimental value can be assumed. The chemical shift anisotropy of 217 ppm corresponds quite well with the spectral range of about 200 ppm reported by Kerkoud et al for low temperature single crystal measurements (19). 

ESR spectra were recorded on JEOL JES-SRE2X at X-band frequency (9.43 GHz), and g-value was determined by third and fourth signals of Mn02 (1.981 and 2.034) as a standard. Low temperature measurement down to 183 K was performed until the freezing temperature of the solution. 

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