The Excitation of Forbidden Spectral Lines

Abstract

Violations of the Bohr selection principles.—(1) A discussion indicates (a) that a breakdown of the azimuthal quantum number rule either with or without a simultaneous violation of the inner quantum rule is not infrequent; (b) that forbidden lines may be produced in absorption and otherwise under circumstances which prove the absence of a strong homogeneous electric field. Violations of the inner quantum rule alone are rare; certain of them may be produced by a strong magnetic field but those found in the present work were produced in the absence of a strong homogeneous field either electric or magnetic. It is suggested that, possibly, rapidly varying inhomogeneous fields are effective. A careful study of the width of these lines and of the variation of the intensity with density might throw some light on the problem. (2) $1S-2p$ group in Hg, Cd and Zn. The forbidden lines $1S-2p_1(\Delta j=2)$ for Hg, Cd and Zn were observed at $\lambda 2270.0$, 3141.1 and 3039.8 respectively and $1S-2p_3$ for Cd at $\lambda 3320.0$ in the positive column of a hot-cathode, low-voltage gradient discharge at low pressure. The intensity of these lines was a maximum at about 250 m-amp/${\mathrm{cm}}^2$, falling rapidly to zero before the current density increased to the point where the sensitive $\mathrm{pd}$ lines show broadening, an incipient Stark effect produced by the fields of neighboring atoms and ions.