Energy level diagrams for the OE and SE. (a) Transition rates important for the OE. (b) Thermal equilibrium population for a two-level spin system. The spin population is depicted schematically in gray. [(c) and (d)] Saturation of the forbidden zero-quantum and double-quantum transitions leads to negative or positive enhancement through the SE.
Dependence of the coupling parameter on the electron Larmor frequency , the correlation time , and the factor . The arrows point out the difference in efficiency at 9 and for . Figure adapted from Loening et al. (Ref. 50).
Population distribution at thermal equilibrium for a general three-spin system (a). Saturation of the allowed EPR transitions for one of the dipolar coupled electrons leads to negative enhancement (b). Saturation of the transition corresponding to the second electron leads to positive enhancement (c).
Top: Growth of the nuclear polarization (open circles—DSE, closed circles—ISE). Figure adapted from Henstra et al. (Ref. 17). Bottom: Enhancement of the nuclear spin polarization as a function of the spin locking time in a NOVEL experiment. Figure adapted from Henstra et al. (Ref. 72).
Illustration of the electron (S) and nuclear (I) spin effective fields. The effective fields belonging to the EPR and NMR transitions are no longer equal. Therefore, four effective fields are needed to accurately describe the two-spin system.
eNCP experiment on perdeuterated BDPA for various settings of and ( at ). CP contact time was set to . Figure adapted from Ref. 19.
Chemical structures of three mono- and two biradical polarizing agents used in high-field DNP experiments.
EPR spectra and DNP field profiles for (a) trityl, (c) TEMPO, and (c) a mixture of trityl and TEMPO. The EPR spectra were recorded in 60:40 w/w at . The DNP samples were prepared in 60:34:6 w/w/w with a total radical concentration of . The solid line represents a simulation of the experimental data. Figure taken from Hu et al. (Ref. 60).
(a) Field profile of TOTAPOL and BT2E recorded at (, rotor). (b) Enhancement profile of -urea as a function of the MW irradiation time in the presence of TOTAPOL ( rotor). Figures taken from Song et al. (Ref. 61).
Present state of vacuum electronic devices in terms of the ability of multiple devices types to generate average power at a certain frequency. Figure taken from Granatstein et al. (Ref. 93).
Left: Schematic of a gyrotron tube indicating its key components. Figure taken from Hornstein et al. (Ref. 14). Middle and right: Photographs of the gyrotron.
Layout of DNP probes. Left: Probe used for DNP in liquids and solids. Figure adapted from Weis et al. (Ref. 115). Right: Low temperature MAS probe for ssNMR DNP experiments. (1) Stator, (2) Sample, (3) Miter bend, (4) Inner conductor, and (5) Outer conductor. Figure adapted from Barnes et al. (Ref. 118).
DNP-enhanced DARR/RAD correlation spectrum of [20% , -GNNQ]QNY nanocrystals. Figure adapted from van der Wel et al. (Ref. 63).
Schiff base region of a typical 2D Lys--Ret.-C15-CX correlation spectrum (DAR/RAAD) of [, ]-bR in the light adapted state . Multiple chemical shift assignments result from a single experiment. . Figure taken from Bajaj et al. (Ref. 62).
In situ TJ-DNP experiment. (a) Pulse sequence. (b) -TJ-DNP NMR spectra of -urea in 50% -DMSO and 50% water . (c) -TJ-DNP NMR spectra of -glucose in . D: 16 spectra of the CO resonance in --proline resulting from a series of TJ-DNP experiments. (Below) average of the 16 spectra giving an improved signal-to-noise ratio. Samples contained TOTAPOL biradical polarizing agent corresponding to electrons. The TJ-DNP spectra (the top traces in each figure) were recorded with a single scan, while the RT spectra were recorded with 256 (a) and 512 scans (b).
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