I. Effect of Gases on the Optically Excited Cadmium I Spectrum

An apparatus producing intense optically excited cadmium radiation is used to study the effects of nitrogen, carbon monoxide, and hydrogen on the optically excited cadmium spectrum, which effects are compared to similar phenomena with mercury. Each gas produces a decrease in the intensity of each of the spectral lines; no increase occurs because of the lack of self-reversal in the lines of the exciting source. The quenching of the resonance line $\lambda 3261$ A.U. is less than that of the remainder of the spectrum. Nitrogen quenches very inefficiently, while carbon monoxide is considerably more efficient: about 35 mm and 3 mm, respectively, of gas pressure are necessary to reduce the intensity of the resonance line to half value. Both of these gases transfer the excited cadmium atom from the $2{}_{}{}^3{}_{}{}^{}P_1^{}{}_{}{}^{}$ to the metastable $2{}_{}{}^3{}_{}{}^{}P_0^{}{}_{}{}^{}$ state by kinetic energy collisions. Hydrogen quenches the cadmium radiation very effectively; a collision between the excited $2{}_{}{}^3{}_{}{}^{}P_1^{}{}_{}{}^{}$ cadmium atom and a hydrogen molecule produces a normal cadmium hydride molecule and a hydrogen atom.