MULTIFREQUENCY ELECTRON SPIN-ECHO ENVELOPE MODULATION SPECTROSCOPY OF META-DINITROBENZENE ADSORBED ON ALUMINA

We report electron spin-echo spectroscopy of a radical species formed upon the adsorption of m-DNB (m-dinitrobenzene) from benzene solution on activated γ-alumina. Two- and three-pulse echo modulation patterns were obtained at sample temperatures of ∼110 K and electron spin excitation frequencies of 6.2, 7.4, 8.2, 9.1, 10.3, and 11.8 GHz. Modulation frequencies are assigned to 27Al, 14N, and 1H nuclei, on the basis of suppression effects, the values of the modulation frequencies, and, particularly, the dependence of the modulation frequencies on external field strength. Aluminum modulations indicate that the radical species formed by interfacial electron transfer is bound to the alumina surface. Through frequency-tracking experiments, we assign the 14N modulation components as double-quantum frequencies and determine hyperfine and quadrupole coupling constants of the observed 14N. The values of these parameters indicate that the adsorbed radical is an ion-pair complex. © 1990 American Chemical Society.