Resonance signal, double

Electron-nuclear double resonance (ENDOR) spectroscopy A magnetic resonance spectroscopic technique for the determination of hyperfine interactions between electrons and nuclear spins. There are two principal techniques. In continuous-wave ENDOR the intensity of an electron paramagnetic resonance signal, partially saturated with microwave power, is measured as radio frequency is applied. In pulsed ENDOR the radio frequency is applied as pulses and the EPR signal is detected as a spin-echo. In each case an enhancement of the EPR signal is observed when the radiofrequency is in resonance with the coupled nuclei. 

This behavior is exploited in SEP experiments [51] where the lowering of the population of level 2 for double-resonance conditions is probed by laser-induced fluorescence (LIF) or ion detection (ion dip experiments) by ionizing the molecules in level 2 with a third laser pulse. It is obvious from the rate equations that no dip depth larger than 50% of the maximum off-resonant signal can be obtained as long as no fast decays of the final levels must be considered. (However, for fast-decaying final levels deeper dips can be expected and the dip depth has been used for an estimate of the decay rate [53].)... 

In the assignment of resonance agnal, the procedures are based prinrarily on the chemical shift values. In additicxi, when multiplets exist, the double resonance method and decoupling by the deuteration of the adjacent hydrogens are used. The disap-pearence of a resonance signal by deuteration is also helpful for tl assigmnent. 

An analysis of a Pto.sRhos with dispersion 0.40 by energy-dispersive X-ray spectroscopy showed that the individual particles had approximately the overall composition. The CO/ Pt double-resonance spectrum of CO close to Pt in the Pto.sRho.s surface is shown in Fig. 40b. The mere existence of this double-resonance signal shows that there is platinum in the surfaces of these particles. Its position, however, is different from that of CO on a pure platinum surface, showing that these particles are alloys. From the analysis of the Pt/ CO double-resonance spectrum of platinum in Fig. 62b, it is found that a fraction 0.49 + 0.07 of the Pt atoms are attached to CO, whereas the dispersion is estimated to be between 0.40 and 0.67 (Sec-... 

In the double resonance experiments, the effect of the deuterium nuclear quadrupole transitions on the NMR signal50 or the NQR signal42 of another nucleus is observed. For example, an ingenious method of detecting pure quadrupole transitions by nuclear double resonance was suggested by Schwab and Hahn.50 In their experiment, the quadrupole transitions of deuterium in a 12 percent deuterium-enriched sample of p-dichlorobenzene were excited, and the effect on the proton resonance signal through dipolar cross relaxation was detected. The 35 Cl spins served to establish and monitor an ordered metastable spin state of the protons. 

When implementing this sequence it may be necessary to add attenuation to the transmitter to increase the duration of each pulse so that the shorter elements do not demand very short (< 1 xs) pulses (note the similarity with the requirements for the DANTE hard-pulse selective excitation described above). The binomial sequences can be adjusted to provide an arbitrary overall tip angle by suitable adjustment of the tip angles for each element. For example, inversion of all off-resonance signals can be achieved by doubling all elements relative to the net 90 condition. Exactly this approach has been exploited in the gradient-echo methods described below. 

In the PMR spectra of the above-mentioned dihydro derivatives the signals of the C-21 methyl and the cyclopropyl methylene protons appear at the normal positions. Therefore the downfield shifts of these proton resonance signals were attributed to the paramagnetic effect from the double bond between C-11 and C-12. Acetylation of 148 and its A-methyldihydro derivative 152 yielded the A, 0-diacetate 153 and the 0-acetate 154, respectively. The negative molecular rotation increment of compound 152 after acetylation confirmed the a-orien-tation of the C-16 hydroxy group. 

Figure 5.18 Diagrammahc representahon of presentahon of data from FT 4D NMR correlahon experiments. In this representation, frequency domain (spectral) information, /nmr(Fi, F2, F3, Ft,) is plotted as a stack or cube of 2D NMR Jnmr(Fi, F4) contour plots, each plot resolved at a different value of f2 and also fs. Double frequency resolution is carried out when single frequency resolution fails to achieve proper signal resolution and/or unique and unambiguous assignment of resonance signals to resonating nuclei.

HSQC) double resonance experiment involving the small globular protein calmodulin, where each plot is resolved at different W-chemical shifts (fa). Off-diagonal peaks indicate inter-residue through-space correlations between W-resonance signals at the given W-chemical shift (fa). Hence HMQC-... 

NOESY-HMQC (HSQC) double resonance experiments can provide unique and unambiguous indications of inter-residue proximities by through-space NOE correlations between pairs of IV H resonance signals. The appearance of symmetrical peaks (see triangulations above) occurs when NOEs are observed between NH systems of amino acid residues with essentially identical chemical shifts to each other (adapted from J. Am. Chem. Soc., 1990, 112, 9020-9022 fig. 2). 

Three infrared-infrared double resonance signals were observed in the Stark spectrum of PD3 for the v=15-14, P(20) line of the CO laser. They are caused by the accidentally overlapped Ri(2) transition in the V3 band and the R2(3) transition in the 2V3-V3 band [2]. 

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