Charles R. Boston

n→π* Electronic Transition in Pure Alkali Nitrate Melts

The lowest‐energy transition (n→π*) of the nitrate ion was found to shift in energy and intensity in a systematic way over the series of molten alkali nitrates from LiNO3 through CsNO3. The energy E of the band maximum varied in a linear way with the cationic radius. At 365°C (extrapolated for CsNO3) E in electron volts was given by (3.81+0.33/r0), where r0 is the cationic radius (Ahrens) in A. The temperature dependence dE/dT was of the order of — 10—4 ev/deg and increased in magnitude with increasing cationic 1/r0. The f number (oscillator strength) decreased steadily along the series of alkali nitrates from 4.1×10—4 for LiNO3 down to 0.86×10—4 for RbNO3 and then rose again to 1.0×10—4 for CsNO3. The thermal coefficient (1/f) (df/dT) was in the range of 10—4 to 10—3 deg—1. The bandwidth changed by only a small amount for changes either in cation or in temperature. The origin of the observed shifts was considered in terms of interionic cohesive forces by application of the Franck‐Condon and conservation ...

Influence of Rare-Gas-Configuration Cations on the Absorption Spectra of Nickel(II) Centers in Liquid Chloride and Bromide Salts

Absorption spectra of dilute Ni2+ centers in melts of CsCl, RbCl, KCl, NaCl, LiCl, MgCl2, CsBr, KBr, and LiBr were measured in the near‐infrared, visible, and, in a few instances, ultraviolet regions. Substantial differences were found in these spectra which correlated with the size of the cations in the solvent salts. The coordination geometry of halides about nickel in CsCl, CsBr, RbCl, KCl, and KBr melts was identified from the spectra as distorted tetrahedral. Coordination geometry in the remaining melts was uncertain. The spectrum for MgCl2 as solvent was very similar to that for LiCl as solvent.

Electronic Spectra and Coordination Geometry in Molten Mixtures of CsCl and NiCl2 Containing up to 60 Mole% NiCl2

Optical absorption spectra (5–26 kK) of fused mixtures of CsCl and NiCl2 containing 2–60 mole % NiCl2 were measured at about 860°C and a mixture containing 20 mole % NiCl2 was studied at 560°—862°C. Up to 20 mole % NiCl2 the Bouguer—Beer law was accurately obeyed, and each nickel was tetrahedrally coordinated to four chlorides. At higher NiCl2 contents, nickel coordination was partitioned between tetrahedral and other (unidentified) geometries. The fraction with tetrahedral coordination progressively decreased with increasing NiCl2 content but was still appreciable at 60 mole % NiCl2. The most prominent feature of the spectrum associated with the unidentified geometries was a band between 18 and 19 kK. These results indicate that nickel has very similar coordination geometries in the liquid and crystalline phases of Cs3NiCl5 but very different coordination geometries in crystalline and liquid CsNiCl3.

Electronic Spectra and Coordination of Nickel Centers in Liquid Lithium Chloride—Potassium Chloride Mixtures

The electronic absorption spectra (4–28 kK) of dilute solutions of NiCl2 in liquid LiCl–KCl mixtures were measured at representative solvent compositions and temperatures from pure LiCl to pure KCl and and from 363° to 1070°C. Phenomenologically the spectra respond to changes in temperature at high temperature and changes in solvent composition at low temperatures in ways that are quantitatively very regular. At intermediate temperatures the behavior is more intricate. The data agree well with the following model. Nickel is partitioned between two types of centers, labeled T and O, which are in equilibrium. The T/O concentration ratio increases with increasing temperature and KCl content in the solvent. At low temperatures the fraction of each kind of center varies linearly with the mole fraction of KCl. The O‐center concentration falls below the detection limit at 900°C in all solvents and in KCl at all temperatures. The coordination geometries of these centers are best described as being distributions a...

ABSORPTION SPECTRA OF FUSED-SALT SOLUTIONS

Studies were made of the ultraviolet absorption spectra of the oxy- anions nitrate, chromate, and nitrate in a variety of fused-salt mixtures. (W.L.H.)

Effect of Melting on the Electronic Spectra of Cs3NiCl5 and CsNiCl3

A method is described for measuring the optical absorption spectra of the crystalline and liquid phases of a transition‐metal salt close to the melting point. Supercooling the liquid permits measuring both phases at the same temperature. This technique was applied to Cs3NiCl5 (mp 547°C) and CsNiCl3 (mp 758°C). It was shown that when Cs3NiCl5 melts, the approximately tetrahedral arrangement of chlorides about nickel is affected only in minor ways, but when CsNiCl3 melts, the octahedral coordination geometry in the crystal is completely destroyed and replaced by a different distribution of geometries. The spectrum of molten CsNiCl3 and its temperature dependence is closely similar to that of nickel centers in molten KMgCl3 at high temperatures. The latter are believed to consist of a single broad distribution of geometries rather than two distinctly separate distributions. It was previously supposed that there are two distinctly different coordination geometries in molten CsNiCl3.

Furnace for Molten Salt Measurements on the Cary Model 14‐H Spectrophotometer up to 1450°C

A resistance‐heated furnace is described which may be used with the Cary model 14‐H spectrophotometer for measuring the absorption spectra of liquid systems at temperatures up to 1450°C. The furnace accommodates a 10‐mm‐square absorption cell and has a platinum liner to contain accidental release of corrosive liquids. The heating element is made of Pt‐20% Rh alloy.