Phase study, spectral series

In electron spin echo relaxation studies, the two-pulse echo amplitude, as a fiinction of tire pulse separation time T, gives a measure of the phase memory relaxation time from which can be extracted if Jj-effects are taken into consideration. Problems may arise from spectral diflfrision due to incomplete excitation of the EPR spectrum. In this case some of the transverse magnetization may leak into adjacent parts of the spectrum that have not been excited by the MW pulses. Spectral diflfrision effects can be suppressed by using the Carr-Purcell-Meiboom-Gill pulse sequence, which is also well known in NMR. The experiment involves using a sequence of n-pulses separated by 2r and can be denoted as [7i/2-(x-7i-T-echo) J. A series of echoes separated by lx is generated and the decay in their amplitudes is characterized by Ty. ... 

The various tautomers and rotamers of alloxan have been examined in detail by the MNDO method and it is predicted that the keto form is most important in the gas phase, although in solution the monohydroxy forms are also thought to contribute. A mass spectral study has been used to investigate the enol-keto tautomeric equilibria of a series of substituted salicylaldehyde and 2-hydroxynaphthaldehyde Schiff bases. In neutral, ethanolic solutions, the cis- and trans-tm forms of 4,5-dimethyl-2-(2 -hydroxyphenyl)imidazoles (393) and (394) have been found to exist in equilibrium in the ground state. However, in neutral aqueous solutions, the trans-eao and keto forms (394) and (395) were the only species detected. Deuterium isotope effects on... 

Mass spectral studies have been conducted on many of the yS-diketonate compounds discussed in this review. Mass spectra of the compounds in the series ML2 (M = Ca, Sr, and Ba L = tpm, ppm, and hpm) have shown that in the gas phase, from a source temperature of 200°C, many oligomeric species, such as [Ca4(tpm)7]+ and [Ca5(tpm)9]+, are present.151 The molecular ion peak corresponding to ML2 was reported to be very small or nonexistent for these compounds. The mass spectral studies of anhydrous Ba(thd)2 (presumably [Ba4(tmhd)g]) have shown that several oligomeric species also exist the ions [Ba4(thd)7]+, [Ba3(thd)5]+, [Ba2(thd)3]+, and [Ba(thd)]+ were detected in the mass spectrum.152 The complexes ML2 (M = Ca, Sr, and Ba L = hfac and tfac) have been... 

A mass spectral study of the 1,1-dihalogeno precursors of (10) and (11) and suitable deuteriated analogues has shown that complete hydrogen scrambling occurs prior to the loss of H or X from the molecular ion. A series of cyclopropyl ethers has been subjected to chemical ionization mass spectrometry and other routine electron-impact studies of cyclopropane-containing compounds are included for completeness. The gas-phase ion chemistry of monosubstituted cyclopropanes has been examined and ion-impact energy-loss spectrometry applied to a series of cycloalkenes including cyclopropene. ... 

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