Continuous-saturation study of spin-lattice relaxation on the “main” and “satellite” lines of an oriented free radical

✍ Scribed by J. Maruani; J. Roncin

• Publisher: Elsevier Science
• Year: 1973
• Tongue: English
• Weight: 401 KB
• Volume: 23
• Category: Article
• ISSN: 0009-2614
• DOI: 10.1016/0009-2614(73)85123-1

✦ Synopsis

Electron-spin relaxation is investigated, through line-shape and continuous-Qturation measurements, in a -/-irmdiated single crystal of glycolic acid at room temperature.

For the only orientation which gives fair line resolution, the experimental data allow determination of the ratio of the effective spin-lattice relaxation times for the "main" and "satellite" lines. Comparison of this ratio with those to be expected from various possible mechanisms suggests that spin-lattice relaxation in this system originates mainly from random modulation, by molecule torsioul oscillations, of the intramolecular dipolar hyperfinc interaction responsible for the spectral pattern.

It has been known for some time [ 1,2] that the weak additional lines which may arise in electron paramagnetic resonance spectra when the hyperfme coupiings of some magnetic nuclei are strongly anisotropic and of comparable magnitude to their Zeeman couplings [3,4] are more difficult to saturate than the usually observed main lines. This phenomenon of differential saturation can be very noticeable at specific orientations of single crystals, but it may also be ob. served in powder spectra through changes similar to, but not to be confused with, those appearing by switching the microwave band. Among the two possible sources for the phenomenon, namely: (i) the smaller microwave-induced transition probability for the satellite lines, and (ii) a possibly larger effective lattice-induced transition probability [S, 61 for these lines, the first was often overlooked. Shimizu [7] was the first to attempt to interpret in detail the phenomenon, taking into account both * An unpublished preliminary account of this work was given at the XVlIeCongb Amp&e (Turku. Finland, August