H-2 ENDOR AND FTESEEM OF THE TANOLD SPIN-PROBE IN AN AMINE-CURED EPOXY MATRIX

Fourier transforms of the electron spin echo envelope modulation (FTES EEM) patterns of deuterated TANOLD spin probes (4-hydroxy-2,2,6,6-pipe ridinyl-1-oxy-d17) in the amine-cured diglycidyl ether of bisphenol A epoxy (DGEBA) at room temperature show two pairs of deuterium lines di splaced about the free deuterium frequency (2.2 MHz) which are assigne d to the electron-nuclear hyperfine couplings of inequivalent -CD3 gro ups of the nitroxide. Conformational asymmetry of the -CD3 groups acco unts for the experimentally observed two pairs of spectral lines at ro om temperature and the disappearance of one pair of lines at 100 K. In this model, it is suggested that two conformational states of the spi n probe molecules are thermally populated as the temperature is increa sed from 100 K to room temperature. Continuous wave electron-nuclear d ouble resonance (ENDOR) spectra support the FTESEEM results. Nuclear q uadrupole interactions, as an alternative explanation for the observed splittings, are shown not to fully account for the experimental obser vations.