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Infrared-absorption spectra of doped KBr crystals at temperatures of approximately 8°K were measured in the wavelength range 2 to 15 μ. From the absorption spectra of crystals doped with NO2− and NO3− ions, and with ions enriched in the isotopes 15N and 18O, frequencies of normal vibrations of six isotopic NO2− molecules, and eight isotopic NO2− molecules were determined. These frequency values were used to calculate a set of force constants for NO2− and NO3− ions in the KBr lattice, using the most general harmonic force field (GFF). In mdyn/Å units, values obtained for NO2− were: fr=7.50, frr=1.66, frα=0.39, fα=1.67, and for NO3−: fr=7.62, frr=1.43, (fα—fαα)=1.09, (frα—frα′)=−0 .48, fγ=1.506. In crystals doped with divalent metal ions as well as NO2− and NO3− ions, new absorption bands appeared. These were perturbations of the vibrational frequencies of NO2− and NO3− ions, caused by association between divalent metal ions and NO2− and NO3− ions. In the case of NO3−, the doubly degenerate asymmetric stretching band was split into two nondegenerate bands by the perturbation, which is thus almost certainly caused by a nearest-neighbor association between metal and nitrate ions. While the other frequency shifts of nondegenerate vibrations can give no information about the symmetry of the surrounding lattice, they can also be explained by a nearest-neighbor interaction between divalent metal and NO2− and NO3 ions.

Zero-phonon transitions of O2−, S2−, Se2− and SeS− molecules in alkali halide crystals were studied by their emission and excitation spectra at 2°K. Most of the information came from emission spectra, which contain large numbers of zero-phonon lines. These lines usually form a single ground-state progression, but extra progressions also appear in most S2− spectra, and in the spectrum of O2− dissolved in KBr. The spectroscopic constants ν00, ω0″, ω0″x0″ and Δ G1/2″ were calculated for all observed progressions, and the Δ G1/2″ values compared with measured Raman frequencies of the molecules. By measuring the effects of uniaxial stress on the emission spectra it was shown that the optical dipole of the emission transition is parallel to the molecular axis, that the axis is parallel to 〈 111〉 directions for O2− in NaCl, KBr and KI, and parallel to 〈 110〉 directions for all other systems, with the exception of the extra emission of O2− in KBr. This dipole could not be so well characterized, except to say that it must lie in a {100} plane. All the emissions are probably due to a Πu2→Πg2 transition. Stress reorientation in the excited state was measured for O2− in KBr crystals. Stress and strain coefficients were calculated for many zero-phonon emission lines; most of the results are in agreement with a linear theory.

The nature of V centers stable at room temperature in KBr crystals has been investigated by means of preferential bleaching with polarized light. V centers were produced by ionizing radiation, by electrolysis with a pointed anode, or by additive coloration with bromine at high pressure. In pure KBr crystals, the properties of V centers depended on the method of production. Two absorption bands of (lOO)-type symmetry were formed at 253 and 278 m/i both by electrolysis and by additive coloration, but no corresponding bands could be found in irradiated crystals. The main product of additive coloration was a broad absorption band extending from the fundamental absorption edge to 320 m/z, appearing in all crystals, pure or doped, which is attributed to bromine molecules. It is suggested that this band forms a large part of the broad absorption band produced by prolonged irradiation of pure crystals, usually referred to as the V% and Vz bands. Furthermore it was shown that the Vz band is not caused by hydride ions. In KBr doped with alkaline-earth impurities an absorption band which does not depend on the method used to introduce V centers appeared at 262 my, in KBr(Ca) and KBr (Si) and at 267 mju in KBr(Ba). This band has (lOO)-type dichroism at 78°K. Optical bleaching of this band at room temperature produced two overlapping bands arising from a common center with (111)-type dichroism at 78°K. Possible models of the centers responsible for these bands are discussed.

Zero-phonon lines in the absorption and excitation spectra of O 2 in molecules in NaCI crystals at 2 OK have been measured. The calculated spectroscopic constants for the first excited state 2n. of O 2 were used to construct potential energy curves, which are compared with recent theoretical calculations.