Relaxation deuterium nuclear

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. 

J. M. Poison, J. D. D. Fyfe, and K. R. Jeffrey,/. Chem. Phys., 94, 3381 (1991). The Reorientation of t-Butyl Groups in Butylated Hydroxytoluene A Deuterium Nuclear Magnetic Resonance Spectral and Relaxation Time Study. 

The stimulated ESEEM experiment is performed at X-band ( 9.5 GHz), which is optimal for echo modulation induced by deuterium nuclei. The stimulated echo is observed after application of three microwave pulses, with the sequence nl2-r-nl2-T-nl2-r-echo. Pulse durations typically are 8 or 16 ns. To maximize the deuterium modulation, the interval r between the first and second pulses is set to t = 1/2vd, where is the deuterium nuclear Larmor frequency. Because is close to 2.2 MHz at X-band, r is close to 220 ns. ESEEM is recorded by scanning the second time delay T. The upper limit for this decay time T ax is determined by echo decay from spin-lattice relaxation typically it is around 10 ps in... 

An important first step in interpreting the C-13 spectra is to distinguish a-carbons from 3-carbons, i.e. methine from methylene. Observation of multiplicity when the proton decoupler is off is one way, but this is not always easy if the lines are broadened by chemical shift multiplicity. Measurement of has been used for this purpose since the 3-carbon with two bonded protons relaxes about twice as fast as the a-carbon with only one. A very positive way is by deuterium labelling. In Fig. 3 is shown the main-chain 25 MHz carbon spectrum of two styrene-S02 copolymers containing 58 mol% styrene, or a ratio of styrene to SO2 of 1.38 (7 ). In the bottom one, 3,3-d2-styrene has been used, cind all the 3-carbon resonances are distinguishable from the a-carbon resonances since the presence of deuterium has eliminated their nuclear Overhauser effect because of this eind the deuterium J coupling ( 20 Hz), they are markedly smaller eind broader than the a-carbon resonances. 

Cu isotopes both with nuclear spin I-3/2. The nucle r g-factors of these two isotopes are sufficiently close that no resolution of the two isotopes is typically seen in zeolite matrices. No Jahn-Teller effects have been observed for Cu2+ in zeolites. The spin-lattice relaxation time of cupric ion is sufficiently long that it can be easily observed by GSR at room temperature and below. Thus cupric ion exchanged zeolites have been extensively studied (5,17-26) by ESR, but ESR alone has not typically given unambiguous information about the water coordination of cupric ion or the specific location of cupric ion in the zeolite lattice. This situation can be substantially improved by using electron spin echo modulation spectrometry. The modulation analysis is carried out as described in the previous sections. The number of coordinated deuterated water molecules is determined from deuterium modulation in three pulse electron spin echo spectra. The location in the zeolite lattice is determined partly from aluminum modulation and more quantitatively from cesium modulation. The symmetry of the various copper species is determined from the water coordination number and the characteristics of the ESR spectra. 

The dominant spin-lattice relaxation mechanism for nitroxides remains unknown. Experimental saturation recovery measurements of the small nitroxides tanone and tanol in an organic solvent in the liquid phase have been published by Percival and Hyde [41]. The values fall in the 10 -10 second range and exhibit an approximately half power dependence on t /T. These authors observed that neither substitution, thereby removing the nuclear quadrupole interaction, nor deuterium substitution affected electron Tj values. 

It is well known that nmr is a powerful means for the study of the dynamics of polymer chains both in solution and in the solid state. The relaxation of 13C nuclei has been extensively employed for this purpose in this and other laboratories. I illustrate here a dilferent and particularly intriguing approach which as yet has seen only very limited application to synthetic polymers. This is deuterium quadrupolar echo spectroscopy, as employed in our laboratory by Dr. Lynn Jelinski and her collaborators (20). The presence of the nuclear electric quadrupole lifts the degeneracy of the two deuterium Zeeman transitions, and in the solid state produces a very broad (ca 200 kHz) powder pattern of transitions which can be interpreted to yield very specific motional information for those carbons labelled with deuterium. In Figure 7 are shown spectra of poly (butylene terephthalate) deuterated on the central carbons of the aliphatic chains ... 

Equation 3 neglects effects of anisotropic motion on both longitudinal and transverse relaxation rates 2). Recent experiments using deuterium NMR on samples similar to those studied here show significant nuclear electric quadrupole splittings that imply an anisotropic component in the water molecule motion ( ). Such motional anisotropy will depress and elevate T]. 

It will be recalled from Equation One that the relaxation efficiency of a donor nucleus is proportional to the square of its magnetogyric ratio - which is why protons are the dominant source of relaxation. Since the magnetogyric ratio of deuterium is only one sixth that of the proton, it follows that replacement of a proton by a deuterium atom effectively eliminates the relaxation contribution from that site. (Because deuterium has a nuclear spin of unity whereas the proton has a spin of one-half, the relaxation contribution from a deuterium nucleus is 6% that of a proton located at precisely the same position.) Thus con5)ari-son of the proton R -values of any derivative with those of a specifically deuterated analog provides a direct measure of a specific interproton relaxation contribution. 

---