Spectrum temperature

The stretching vibration Vio at about 440 cm has four Raman active components in the crystal. However, in the low temperature spectra there is... 

Valence Isomerism. Restricted Rotation and Permutational Isomer i sm. - The variable temperature spectra of bicyclic tetraphosphines (29) has been analysed in terms of valence isomerism involving the corresponding two coordinate open-chain isomers.62 A report on ab initio MO calculations of the inversion barriers for a series of methyl phosphines includes a discussion of the electronic consequences of steric effects.63 Inversion barriers of 1,2-diphosphinobenzenes are in the range 100 - 110 kJ mol". 66 The ring inversion barrier for a dibenzophosphorin has also been measured.63... 

CD] lxlO 3 M [substrate] 1 M room temperature, spectra measured after 30 min, d-doublet, s-singlet l-Phenyl-l,2-propanedione. 

Fig. 6. Spectral monitoring of the thermal denaturation of the highly helical, Ala-rich peptide Ac-(AAAAK)3AAAA-YNH2 in D20 from 5 to 60°C, as followed by changes in the amide V IR (left) and VCD (right). IR show a clear shift to higher wavenumber from the dominant a-helical peak (here at an unusually low value, 1637 cm-1, due to full solvation of the helix) to a typical random coil value ( 1645 cm-1). VCD loses the (—,+,—) low-temperature helical pattern to yield a broad negative couplet, characteristic of a disordered coil, at high temperature. Spectra were normalized to A = 1.0 by 45°C.

Thermally denatured proteins have been studied for a variety of systems using FTIR and VCD. The resulting high-temperature spectra often reflect the characteristics seen earlier for random coil peptides as well as that seen for the unstructured casein. Particularly the amide I IR bands show a frequency shift to center on a broadened band at 1645-50 cm-1. The amide I VCD loses its distinctive character (Fig. 11) and tends toward... 

Figure 8 Plot of low frequency Raman spectra of a high molecular weight linear polyethylene that was initially quenched at —70°C as a function of temperature. Spectra obtained at (a) room temperature, (b) 57°C, (c) 87°C and (d) 147°C. Reprinted with permission from Ref. [102]. Copyright 1986 American Chemical Society.

The behaviour of the CD of (3R,3 R)-zeaxanthin at low temperature can also be explained on the basis of simple conformational considerations. On lowering the temperature, the most stable form becomes more populated and gives a predominant contribution to the spectrum. Obviously there may be instances where the CD as a function of temperature is much more complicated than that just discussed, one example being (3S, S S j-astaxanthin. However, the low-temperature spectra can be interpreted even here by... 

The absorption spectrum measured in the typical pump-probe experiment is the difference between the spectrum of the remaining irradiated precursor and the created intermediate(s). Assignment of the transient absorption spectrum typically is done by reference to the low-temperature spectra described above, and (sometimes more certainly) by analysing the chemical behavior of the intermediate. For example, many carbenes are known to react with alcohols to give ethers (see below). If the detected intermediate can be observed to react with an alcohol, then this is taken as additional evidence for its assignment as a carbene. 

The approach presented in this work can be also extended to the case of Dirac and Klein-Gordon operators, too in order to calculate finite-temperature spectra of heavy-light and hybrid mesons. 

P NMR data have been reported for Ir4(CO)8(PPh2Me)4 [6 -8.4(1), —40.6(2), 61.6(1) p.p.m.] together with a variable temperature H NMR study, which indicates that phosphine intra-exchange occurs at high temperatures whereas the low temperature spectra are consistent with a number of alternative stereochemical arrangements46. ... 

Pseudorotation.—A number of spirocyclic phosphoranes possess square-pyramidal structures rather than the trigonal-bipyramidal structures previously assumed, and this could have important consequences on the interpretation of their variable-temperature spectra. There is, as yet, no evidence that acyclic or monocyclic phosphoranes favour the square-pyramidal geometry, and the variable-temperature XH... 

Figure 4.22 IR spectra of NHJ-FAU zeolite (Si/Al2 = 5.5) after 1 h treatment in flowing He at various temperatures. Spectra collected at 25°C. HF-OH is in supercages, LF-OH in sodalite...

Room temperature spectra were taken over the range of pressures 1-760 torr. Typical results obtained are plotted in Figure 4 along with the calculated fit of the data points to a Langmuir adsorption i sotherm. 

Figure 1.23 Variable temperature spectra in the olefinic and B-H regions of the NMR...

The P H HP NMR picture of CO/ethene copolymerisation in MeOH is exemplified by the sequence of variable-temperature spectra shown in Figure 7.6 relative to a reaction catalysed by [Pd(TFA)2(dppp)]. It has been observed that the intensity of the P NMR signal decreases with time, which is apparently due to the irreversible reductive degradation of Pd" species to Pd metal [5b, c]. 

Knight shift in, 4 288 low-temperature spectra, 32 29 measurement of, and periodic table, 18 198-202... 

The spectrum of bis(acetylacetonato)oxovanadium(IV) (Fig. 7) shows two low-intensity absorption bands (e 10—100) in the 10—20 kK region, at about 14 (band I) and 17 kK (band II) 23). Low-temperature spectra reveal a splitting of band I into three bands 23) either electronic 20, 23) or vibronic (24) in origin. Another band (band III) is found at about 25 kK. Recently, beautiful vapour-phase spectra of several five-coordinate bis(j9-diketonato)oxovanadium(IV) have been recorded (25). 

Fig. 5. The 13C nuclear magnetic resonance line widths of the (enriched) choline methyl resonances in dipalmitoylphosphatidylcholine (A) and in dielaidoylphosphatidylcholine (O), as a function of temperature. Spectra taken at 90.5 MHz similar results were also obtained at 25.2 MHz. Note that the higher-melting lipid, dipalmitoylphosphatidylcholine, shows a readily observable enhanced line broadening at temperatures TU 32°C, corresponding to the onset of the lateral phase separation. (Data from Ref. 4.) [Reprinted with permission from P. Brulet and H. M. McConnell, J. Am. Chem. Soc., 98, 1314 (1977). Copyright by American Chemical Society.]...

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