Abstract

Investigations of the infra-red spectra of thorium were undertaken in order to establish a correlation between the two previously established but unconnected energy groups in the Th II term structure. Specially sensitized infra-red plates were exposed in a thirty-five foot Wadsworth stigmatic grating spectrograph to sparks between metallic thorium rods and to high current arcs of thoria in carbon and copper electrodes. Many strong arc and spark lines were recorded in the region λ8665A to λ11230A. The desired combination lines were observed and readily established the correlation between the two previously distinct groups of levels. The separation of the low levels ${{}^{2}D}_{1\frac{1}{2}}$ (from 6d7s²) and ${{}^{2}F°}_{2\frac{1}{2}}$ (from 5f7s²) was found to be only 4490.29 cm⁻¹. Infra-red quartet multiplets as well as quartet multiplets involving the most sensitive lines of Th II are presented and discussed. Tables of infra-red wave-lengths and of spectral terms are given in detail.

© 1945 Optical Society of America

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