Spectra temperature dependence

The temperature dependent spectra of PBLG-d5 is shown in Fig. 6. Line shapes below — 76°C are similar to the rigid state pattern, indicating the absence of fast and large-amplitude motions. They are, however, different in... 

Similar temperature-dependent spectra were obtained after evacuation following the adsorption of on Pt/Al203. However, it was also found that exchange with OH groups of the support led to a proportion of r>CH absorptions at both ca. 3025 and 2947 cm 1 (and corresponding yOD absorptions) in addition to the strong i CD absorption at 2260 and 2200 cm 1. Such exchange occurred even at room temperature and quantitatively favored the 2947-cm 1 species. 

Fig.2 shows the absorption spectrum of Er2BaNiOs. Optical spectra of all the members of (ErxYi.x)2BaNiOs series are very similar for the temperatures above TN announcing a similarity of the crystal field at the Er site. The analysis of the temperature-dependent spectra of a series of samples with x=0.1, 0.2, 0.4, 0.6, 0.8, and 1.0 enabled us to determine a reliable scheme of... 

Figure 12.11 The temperature dependent spectra of Figure 12.10 are fitted with two lines with variable width and chemical shift. Here the line width of both lines are shown as a function of temperature...

Temperature-dependent spectra (240). Hot atom chemistry reported (117). m 1 JMoP data (10, 258). 

As expected for one rotamer, the spectra of 3 do not change with temperature. In the Raman spectra of 1 one would expect from the calculations to see some changes with temperature. However the temperature-dependent spectra of 1 give no unambiguous evidence for the existence of more than one rotamer. 

The temperature-dependent spectra were interpreted in terms of a two-site hop model, in which the deuterons undergo jumps through a dihedral angle of 103°. This type of motion is consistent with gauche-trans conformational transitions. At -88"C these motions appear static on the time scale of the deuterium NMR experiment, and at +85 °C the motions are in the fast exchange limit. The rate constants for these motions were obtained from the calculated spectra. An Arrhenius plot of these data show that the apparent activation energy is 5.8 kcal/mol. (Dynamic mechanical data (20 Hz) fall on the Arrhenius plot.) The transitions have an intermediate rate on the deuterium NMR time scale at 20 °C, with the correlation time for the motion being 7 x 10 6 s at this temperature. 

The samples for NMR spectroscopy were melted into glass tubes and allowed to cool from the melt. The observed deuterium NMR spectra are reproducible with temperature cycling, thus providing evidence that the thermal history induced by acquiring temperature-dependent spectra of the samples does not greatly affect the properties that we are measuring. 

The low temperature spectra 11X> of two substituted [18]annulenes, the nitro and the acetyl derivatives (22 and 23 resp.), are also indicative of aromatic compounds, as they show the characteristic shielding of the six inner protons and the deshielding of the eleven outer protons. On warming these solutions the spectra do not coalesce to a singlet, but rather seem to represent the coalescence of only some of the protons (c.f. the temperature-dependent spectra of some substituted [16]-annulenes 106>). Thus, for 22 about five protons remain permanently in an external position (t 1.4 to 2.0, area 4.7) whilst the remaining twelve protons are averaging (t 6.7, broad band, area 12.3). This can be explained in terms of the three possible conformers of a mono-substituted [18]annulene, 18a-c X11>. If R is a bulky group the conformer in which it... 

Figure 13. The NMR spectra (200MHz, CDjCN) of the isomeric copper(I) conq>lexes of the tetradentate bispidine ligands 14 and 35 (a) temperature dependent spectra of [Cu(14)(NCCH3)]+ ...

Analysis of exchange-broadened NMR spectra (that is, the simulation of temperature-dependent spectra as a function of the exchange rate) has become the method of choice for the determination of the free activation enthalpy for intramolecular conformational equilibria and for intermolecular exchange processes. Studying, in addition, the pressure dependence of the... 

Thermodynamic considerations suggest that such transformation phenomena are thermally controlled. In fact, amorphous phase coatings spontaneously crystallize above some critical temperature. The transformation is manifested in the Raman spectrum by dramatic band intensity increases and marked band narrowing (20). When metastable crystalline treated, recrystallization temperature phase occurs as the temperature-dependent spectra shown in Figure 13, which depicts the irreversible transformation of anatase to rutile in a thin titania film. 

The C NMR CP MAS spectra of 2-naphthylphenylsulfoxidein the solid state were used to study the restricted rotation about the Ph-S bond. Line shape simulations of the temperature-dependent spectra allowed the corresponding barrier to be determined in the solid state (14.7 kcal mol" ). It was shown that by using the single-crystal X-ray structure, this barrier could be satisfactorily reproduced by theoretical calculations (14.5 kcal mol" ) that take into account the correlated phenyl motion involving a large set of molecules in the crystalline state. 

AHpp decreases from "2.5 G to "0.7 G. This is consistent with increased mobility for the charge carriers as the lattice vibrations are slowed down. Similar temperature dependent spectra have been observed for monovalent doped polyacetylene (28). 

The temperature-dependent spectra measured from 140 to 280 °C (in 1 °C increments) are illustrated in Fig. 7a, b. Figure 7a is a contour map looking down from above, while Fig. 7b is the ordinal expression. Each colored line in Fig. 7a indicates a noteworthy vibrational band. 

---