Spin slate changes

Figure 6.30. Enhancement of the proton NMR signal amplitude (P/P -l) is shown as a ftinction of microwave frequency as taken by the dynamic nuclear polarization experiments, where P and / are the signal amplitude with and without microwave pumping, respectively [143,146,173,174], The Overhauser effect (OE) typical to the mobile spins makes a shaip peak at the Lannor frequency cve of the electron spin but the Solid State Effect (SSE) shows two extrema separated by o from (O charactcrictic with the fixed paramagnetic spins [8], The solid curves are a guide for the eye. (a). t a is-(CH), (A//pp 0.8 G) and , trs-rich (CH)> (Affpp 7.8 G) 1174]. (b) The temperature dependence of the peak-ratio in //ww-(CH), 173], y/x = 0 means pure Overhauser enhancement and y/x— 1, the solid slate effect [173]. Note the change from the mobile above 150 K to the trapped below 150 K, Most of the solitons are trapped below 10 K, (after (a) [174] and (b) [173])...

A second selection rule stales that any Irataiiion for which S 0 is forbidden-. i.e.. in order to be allowed, a transition must involve no change in spin stale. Looking at the correlation diagram fora d configuration in an octahedral field (Fig. I I.3S), we note that the groiiiid slate has a multiplicily of 3 (5 = I) and that there ate three excited stales with this same multiplicily A3, and (bom Ihe / ). Thus we... 

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