The infrared arc spectra of manganese and rhenium

New types of photographic plates sensitive to infrared radiation arc employed to explore the long-wave portions of manganese and rhenium arc spectra from 7,200 to 11,000 A.The sources were metallic manganese in a copper arc and metallic rhenium in a silver arc.The spectrograms were made with large con- cave grating spectrographs, the first half of the range being investigated with a threefold increase in dispersion and resolution.Many new lines have been recorded in each spectrum and these in turn have disclosed new spectral fcerma or atomic energy levels.Lines in both spectra exhibit hvperfine struct CONTENTS Page I. Introduction 757 II.Apparatus and methods 758 III.Results 759 1. Manganese 759 2. Rhenium 766 I. INTRODUCTION Metallic manganese was first isolated in 1774 and for 151 years remained the only known metal with a maximum valence of 7.Nearly a century after its discovery, MendeleefT predicted, on the basis of a periodic arrangement of the elements, that 2 liomologues of manganese should exist.These hypothetical elements were referred to as eka-manganese and dwi-manganese, or more recently as atomic numbers 43 and 75, until they were finally captured in 1925 by Nod- dack and Tacke, 1 and renamed masurium and rhenium, respectively .At the present time the amount of concentrated masurium ir> probably still too small for the study of its optical spectra, so that manganese and rhenium are the only metals of Group VII available for spectro- scopic study.Although the spectra of manganese have been under investigation since 1864, they are still far from being in a satisfactory si ate, especially at their extremes.The longer wave portion of the manganese arc spectrum was investigated by Kiess and Meggers 2 in 1920 with dicy- anin sensitized emulsions but even with 5-hour exposure only four lines beyond 9,000 A were detected.The first extensive description and analysis of the rhenium arc spectrum was published by Meggers 3 in 1931, but the observations