Broad Lines in the Arc Spectrum of Copper

Attention is called to the anomalous broadening behaviour of certain lines in the copper arc spectrum, particularly those arising from initial terms $c^4{D}_{2,3}$. Breadths of several lines have been measured with copper arc spectra and pressures up to eighty atmospheres. The following are the most essential conclusions drawn:-(a) broad lines with the same initial term have the same breadth, (b) all lines show a linear increase of breadth with increasing pressure, (c) lines arising from $c^4{D}_{2,3}$ terms have a considerable breadth at zero pressure. The intensity contours of $\lambda \lambda 4378$, 4539 and 4587 ($c^4{D}_{2,3}$ lines) at one atmosphere have been determined and found to have a form represented by the formula $\frac{a^2}{[{(\lambda -{\lambda }_0)}^2+a^2]}$. The discussion touches on the nature and cause of the breadth of some of the copper lines, it being concluded that the breadth is an inner property of the copper atom, i.e., not due to external disturbances. The effective diameter of the copper atom would need to be increased considerably by excitation if the pressure broadening is to be accounted for by the Lorentz collision effect.