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The presence of gold atoms in the silicon lattice decreases the lifetime of excess electrons and holes in p-and w-type material. The capture of electrons in ^-type silicon occurs through the gold donor level with a capture cross section, o-n0 , of 3.5X10" 15 cm 2 (at 300°K). This capture cross section varies as r~2-5 between 200° and 500°K. In w-type silicon the electron capture cross section, o-n0 , is 5X10~1 6 cm 2 at 300°K and is temperature independent; the hole capture cross section, o-p0 , is 1X10~1 5 cm 2 at 300°K and varies as r~~4. The capture in this case occurs through the gold acceptor level.

Electron nuclear double resonance (ENDOR) spectroscopy has been used to study protons in nitrosyl horse heart myoglobin (MbNO). (1)H ENDOR spectra were recorded for different settings of the magnetic field. Detailed analysis of the ENDOR powder spectra, using computer simulation, based on the "orientation-selection" principle, leads to the identification of the available protons in the heme pocket. We observe hyperfine interactions of the N(HisF8)-Fe(2+)-N(NO) complex with five protons in axial and with eight protons in the rhombic symmetry along different orientations, including those of the principal axes of the g-tensor. Protons from His-E7 and Val-E11 residues are identified in the two symmetries, rhombic and axial, exhibited by MbNO. Our results indicate that both residues are present inside the heme pocket and help to stabilize one particular conformation.

The Q-band (35 GHz) electron paramagnetic resonance (EPR) spectra of nitrosyl hemoglobin (HbNO) and nitrosyl myoglobin (MbNO) were studied as a function of temperature between 19 K and 200 K. The spectra of both heme proteins show two classes of variations as a function of temperature. The first one has previously been associated with the existence of two paramagnetic species, one with rhombic and the other with axial symmetry. The second one manifests itself in changes in the g-factors and linewidths of each species. These changes are correlated with the conformational substates model and associate the variations of g-values with changes in the angle of the N(his)-Fe-N(NO) bond in the rhombic species and with changes in the distance between Fe and N of the proximal (F8) histidine in the axial species.

PHYSICAL REVIEW LETTERS JANUARY 15, I960and a field of E /W 0 is assumed. It can easily be shown that if the phenomenological law,

Articles you may be interested inSpin-dependent recombination electron paramagnetic resonance spectroscopy of defects in irradiated silicon detectorsElectron spin resonance has been observed in n-type silicon irradiated with O.S-Mev electrons. The particular resonance lines discussed here appear only in pulled crystals which contain about 10 18 oxygen atoms per cm a • The lines do not appear in floating zone crystals « 10 17 oxygen per cm a ). The pattern is anisotropic with respect to the field orientation and can be fitted with a g tensor with components g[lOO] =2.0029, g[llO] = 2.0019, g[110] = 2.0096.Hyperfine structure due to interactions with Si 29 nuclei is also observed. The hyperfine structure tensor exhibits a [l11J symmetry indicating that the electron is not centered on the silicon nucleus with which it is interacting. A model is suggested, consistent with the observed symmetries, according to which vacancies produced during irradiation diffuse to the distorted regions around oxygen atoms.

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