s enhanced in the Pb(+) bias and suppressed in the Pb(-) bias, and (b) this enhancement and suppression effect increases with decreasing electron concentration of the Si electrodes, i.e. , with increasing asymmetry in the normal conductance.In normal metal-oxide-superconductor junctions, the normal conductance seldom varies by more than 5% over the phonon energy range of the superconductor. The asymmetry effect discussed here is, therefore, negligible and (dI/dV), /(dI/dV)" measures Ns directly. In contrast, the normalconductance asymmetry observed in Si-Pb junctions is common to most degenerate semiconductorsuperconductor contacts. Since the asymmetry can be controlled by properly choosing the carrier concentration of the semiconductor electrode, it should be possible to utilize this enhancement effect to study the fine structure in Ns of the more weakly coupled superconductors, e. g. , Al and Zn, which has not been possible with metal-oxide-metal junctions.Electron-spin-resonance investigations of the Mn ' center in BaF2, CdF2, and SrF2 are reported and spin-Hamiltonian parameters are given. Previously reported values for the Mn~' center in CaF2 are given for comparison.We have recently reported' a critical analysis of the ESR spectra obtained from the Mn~' center present in dilute concentrations in CaFz. As a result, several uncertainties associated with earlier investigations have been resolved and accurate values for the spin-Hamiltonian constants of this system have been determined.This addendum reports the results of our subsequent ESR investigations of the Mn~' center in the isomorphic hosts BaFz, Sr', and CdF~. Single-crystalline samples of BaF3, SrF~, and CdF& were obtained from Optovac, Inc. The ESR data obtained from the samples of SrF3 and CdF~, both containing nominally 10 ' wt% Mna', exhibited fluorine superhyperfine structure similar in resolution and appearance to that observed in the CaF~system. These data were analyzed in a manner closely following that employed for CaF~, which was described in detail in Ref. 1. The best-fitted spin-Hamiltonian parameters to the experimental data are shown in Table I, in which we include the results of CaF3 for comparison. The ESR spectra observed in the BaF2 crystal with a ]. 0-'-wt%-Mna' concentration also displayed TABLE I. Room-temperature spin-Hamiltonian parameters, lattice constants (r), observing ESR microwave frequencies (f), and linewidths (hH) «r Mn' in CaF2, BaF2, SrF2, and CdF2. Host C aF2 BaF2 Sr F2 Cd F2