II. Optical Excitation of Cadmium Hydride and Zinc Hydride Bands

Excitation of a cadmium-hydrogen gas mixture with light from a hydrogen-cadmium electric discharge produces with great intensity a portion of the band system of the CdH molecule, while excitation of the same mixture with light from a helium-cadmium discharge does not produce these bands. The process consists, first, of a collision between a $2{}_{}{}^3{}_{}{}^{}P_1^{}{}_{}{}^{}$ cadmium atom and a ${\mathrm{H}}_2$ molecule to form an unexcited CdH molecule, which molecule is then brought to the excited levels by absorption from the exciting light of the band frequencies themselves, whence it emits the band radiation in returning to the normal state. A weak excitation of the entire ${}_{}{}^2{}_{}{}^{}\Pi -{}_{}{}^2{}_{}{}^{}\Sigma$ band system also occurs independently of the optical excitation as a result of collisions of the second kind with excited cadmium atoms.