Experimental spectra recording

The detection system depends on the concentration of absorbing atoms in the material and photon energy. For bulk experiments using hard X-rays (i.e., with hv  

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The most substantial investigation of thallium(II) species in aqueous solution is that of Dodson and Schwarz, who studied equilibria and kinetics of Tl(II)-Cr complexes (77). On the basis of some (reasonable) assumptions, they have calculated the stepwise stability constants K for the three T1C1 " complexes, n = 1,2,3, in 1M HCIO4 and estimated = 1 from the ratios between the stability constants K, for Tfi Cl " and TT C1 ". The absorption spectra of the individual Tl(II) chloride complexes have been derived from their stability constants in combination with the experimental spectra recorded for solutions with varying composition. Absorption maxima were found at 263 and 342 nm for TlCl, at 280 and 342 nm for TICI2, and at 304 and 362 nm for TlCla". An interesting observation was the 10-fold increase of the extinction coefficient (at —340 nm) of the Tl(II) solution in 1 M perchloric acid upon addition of a small amount of chloride ion ([Cl ] = 10 M) (77). 

One recent example is a HF EPR study of nitroxide side-chain dynamics in a helix-forming peptide which was labeled with MTSSL." The experimental spectra recorded at 140 GHz from 277 to 306 K were found to be amenable to... 

Fig. 5-9. (a) The experimental spectrum recorded 0.5-1.0 ps after radical creation through... 

Figure 4. Correlation of the chemical shielding and C—H dipolar coupling tensors of the formate group of 50% C-enriched methyl formate powder, a. Computer calculated 2D spectrum for a = 33° and p = 85°. b, Experimental spectrum recorded at 25-MHz C resonance and 90 K. The 2D spectrum permits the determination of the relative orientation of two molecular interaction tensors without the need of growing single crystals. (Reproduced, with permis n, from Ref.

Fig. 5-9. (a) The experimental spectrum recorded 0.5-1.0 (is after radical creation through photolysis of acetone in diethyl phosphite, (b) Tbe calculated stick spectrum employing only the STo polarization, (c) The calculated stick spectrum employing only the ST.i polarization, (d) A S >ectrum calculated by adding spectra (b) and (c) in almost equal proportions, with some added net absorption. (Reproduced from Ref. [18] by permission from Elsevier Science B. V.)... 

There are 78 vibrational degrees of freedom for TgHg and it has been shown that the molecule has 33 different fundamental modes under Oh symmetry, 6 are IR active, 13 are Raman active, and 14 vibrations are inactive. The experimental fundamental IR active vibrational frequencies have been assigned as follows 2277 (v Si-H), 1141 (vas Si-O-Si), 881 5 O-Si-H), 566 ( s O-Si-O), 465 (v O-Si-O), and 399 cm ( s O-Si-O). These generally agree well with calculated values The IR spectrum recorded in the solid state shows bands at 2300 and 2293 cm ... 

Fig. 12b). Since practically the same spectral shape is obtained at Q-band (35 GHz) (Fig. 12c), the commonly used criterion stating that the shape of an interaction spectrum is frequency-dependent fails to apply in this case. Actually, outer lines arising from the exchange interaction are visible on the spectrum calculated at Q-band (Fig. 12c), but these lines would be hardly detectable in an experimental spectrum, because of their weak intensity and to the small signal-to-noise ratio inherent in Q-band experiments. In these circumstances, spectra recorded at higher frequency would be needed to allow detection and study of the spin-spin interactions. 

For the NFS spectrum of [Fe(tpa)(NCS)2] recorded at 108 K, which exhibits a HS to LS ratio of about 1 1, a coherent and an incoherent superposition of the forward scattered radiation from 50% LS and 50% HS isomers was compared, each characterized by its corresponding QB pattern (Fig. 9.16) [42]. The experimental spectrum correlates much better with a purely coherent superposition of LS and HS contributions. However, this observation does not yield the unequivocal conclusion that the superposition is purely coherent, because in the 0.5 mm thick sample the longitudinal coherence predominates since many HS and LS domains lie along the forward scattering pathway. In order to arrive at a more conclusive result, the NFS measurement ought to be performed with a smaller ratio aJD on a much thinner sample. Such an experiment would require a sample with 100% eiuiched Fe and a much higher beam intensity. 

Carotenoid neutral radicals are also formed under irradiation of carotenoids inside molecular sieves. Davies and Mims ENDOR spectra of lutein (Lut) radicals in Cu-MCM-41 were recorded and then compared with the simulated spectra using the isotropic and anisotropic hfcs predicted by DFT. The simulation of lutein radical cation, Lut +, generated the Mims ENDOR spectrum in Figure 9.7a. Its features at B through E could not account for the experimental spectrum by themselves, so contribution from different neutral radicals whose features coincided with those of the experimental... 

The experimental spectrum in Figure 12.4 was recorded for a sample temperature of circa 20 K. Upon lowering of the temperature, and concomitantly reducing the microwave power to avoid saturation, one finds that the normalized intensity of the spectral features diminishes. At 10 K the lines with gtU = 10.5 and 5.5 are gone and only the geff = 5.8 peak remains at 4.2 K also this latter feature has disappeared the doublets that give rise to these transitions (l l/2) and l 3/2), respectively) have been... 

FIG. 7. Experimental and simulated room-temperature (20 °C) X-band CW-EPR spectra of a mixtures of Cr(VI) and lactose (15), pH 5.0. Spectrum recorded 24 h after mixing, mod. ampl.=0.04 mT, microwave frequency 9.7 GHz. Figure is adapted from ref. 70. 

Figure 3.18 compares the spectrum of D2-Ar recorded at 165 K at a density of 142 amagat with an H2-Ar spectrum recorded at the same temperature and 150 amagat argon density [109]. As expected, we see more rotational lines, So(J) with J = 0,. ..4, than for H2-Ar, and these have different relative intensities. The rotational lines are also sharper, roughly by the factor 1/ /2. The spectral moment Mo is the same as for H2-Ar, well within the experimental uncertainties, as it should be. 

Whether the relaxation is fast or slow at 4.2 K can be checked experimentally, using the following arguments. Figures 2.6b shows a 4.2 K Mossbauer spectrum recorded for B = 8.0 T. The solid line outlines the contribution of Z. The remaining absorption pattern, well understood, originates from the [Feni(H20)6]3 + contaminant. The sharpness of the absorption lines of Z shows that the intermediate has nearly axial symmetry thus, we can set EID = 0 in Equation 2.2 and Ax = Ay in Equation 2.3. We have recorded, and published, spectra in variable applied fields and at different temperatures.11 Since the spectra are a bit noisy, it will aid the reader if we... 

FIGURE 2.13 Mossbauer spectrum of intermediate X recorded at 80K in a parallel applied field of 8.0 T, same experimental spectrum in all panels. Solid lines in (a) and (c) are spectral simulations for sites a and b assuming diamagnetism that is, Bint = 0. The solid fines in (b) and (d) were obtained by adding, in both cases, a negative Bint. The solid fines are actually simulations for the full Hamiltonian of Equation 2.1 for a ferromagnetically coupled center. The sum of the theoretical curves in (b) and (d) fits the experimental spectrum quite well. 

The lower panel of Fig. 5 shows the experimental tunneling spectrum recorded in the middle of a large terrace of a Cu(lll) surface. The differential conductivity at constant tip height shows an onset (defined as the midpoint of the rise) at —440 40 meV, which corresponds to the step-like increase in the 2D LDOS at the bottom of the free electron-like surface state. 

Equation (9.1) allows us in principle to draw a spectrum that matches the entire spectrum obtained experimentally. This is correct only if the recorded spectrum originates from one fluorophore (i.e., Trp in solution) or from compact protein within a folded structure. However, when the experimental spectrum originates from two fluorophores (i.e., mixtures of tyrosine and tryptophan in solution) or from a disrupted protein that has two classes of Trp residues, the calculated spectrum using Equation (9.1) does not match the recorded spectrum. 

If the computer is equipped to provide output of data on a cathode-ray tube, a camera may be used for recording a series of theoretical spectra computed from various sets of parameters, thus simplifying the search for a trial, theoretical spectrum that resembles the experimental spectrum.242 Output options for n.m.r. programs now include tables of energy levels and error parameters, and lists of progressively and regressively connected transitions that can be correlated with double-resonance experiments (see Part II, Section VI). 

Fig. 8.2. (a) Spectrum of He-like argon obtained on tokamak TEXTOR open points - experimental spectrum, dashed line - theoretical fit. Spectrum was recorded at 3.7-4.7 s, Te = 1.1-1.2 keV. (b) Spectrum of He-like iron from the tokamak Tore Supra open points - experimental spectrum, dashed line - theoretical fit. Spectrum was recorded at time 4.0-6.0 s, Te = 2.0-2.2keV... 

Figure 15 (a) The 4.2 K Mossbauer spectra of [(Fe(IV)=0)(TMC)(NCCH3)](0Tf)2 in acetonitrile recorded in (A) zero field and (B)a parallel field of 6.5 T. The solid line represents a spin Hamilton simulation with the parameters described in the text, (b) Mossbauer spectra of [Fe(lV)=(0)(TMCS)] recorded at temperatures and applied fields that are indicated. The solid lines represent spin Hamiltonian simulations with parameters described in the text. The spectra were simulated in the slow (at 4.2 K) and fast (at 30 K) spin fluctuation limit. The applied field was directed parallel to the observed y radiation. The doublet drawn above the topmost experimental spectrum (0 T, 4 K) represents a 7% Fe(ll) contribution from the starting complex. (From J. U. Rohde et al. (2003) Science 299 1037-1039. Reprinted with permission from AAAS)... 

FIG. 12. Temperature-dependent Be NMR spectra in Be(TMPA)J, recorded in the pulsed mode at 12-2 MHz in trimethyl phosphate (TMPA) (a) simulated, (b) experimental spectrum. (106)... 

Figure 6. ESR spectrum recorded on reaction of OH with 0.2 mM compound b in an N20-saturated aqueous solution at pH 2 and ca 5 °C. The experimental spectrum from the four equivalent methylene hydrogens and the two equivalent aromatic hydrogens is shown in the lower part the upper part contains the lines from C in natural abundance. S. Steenken, unpublished material.

Fig. II. (a) Experimental and (b) numerically simulated ° Zn QCPMG spectra of zinc diimidazole diacetate. The experimental spectrum was recorded at 11.7 T using 24,000 transients with a recycle delay of 2 s. The simulated spectrum used Cq = 8.2 MHz, tjq = 0.62, and iso = 155 ppm (relative to a 0.9 M solution of Zn(OOCCH3)2 2H2O). Reproduced from Ref. 144 with permission.

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