Bands in the Spectrum of Boron Hydride

Abstract

WITH the object of obtaining band spectra due to compounds of boron, we have investigated the radiation emitted by a condensed discharge in a tube through which a stream of BCl₃ was passed. Besides the atomic lines of boron, chlorine, aluminium (from the electrodes), and hydrogen (perhaps due to HCl present in the BCl₃), we found a number of widely spaced bands in the neighbourhood of 4000 A., which we ascribe to the molecule BH. Photographs taken in the first order of a 21 ft. concave grating showed that these bands consist of single P-, Q-, and R- branches, the Q-branch containing a considerable number of lines, and the lines P(0), P(1) being missing. The bands must hence be considered as a ¹II→ ¹∑ transition, probably corresponding to the ¹II→¹∑ transition observed for A1H by Eriksson and Hulthén.¹ The P- and R-lines of the strongest band are accompanied for higher rotational quantum numbers by weak satellites due to the isotopic molecule B¹⁰H. The frequencies of the principal lines, emitted by the molecule B¹¹H, may be represented with good approximation by writing for the rotationa terms of the ¹II-state