Excitation of the lines of Mg+ in low-voltage, low-current discharge. The stronger lines of Mg+ appear at potentials equal to the ionization potential of Mg plus the excitation voltages predicted from their classifications. This proves that a single impacting electron can ionize an atom and raise a valence electron of the ion to a higher orbit.
Excitation of the pp′ lines of Mg and Cd in low-voltage, low-current discharge. Using a quartz spectrograph to analyze light from the force-free space between grid and plate, it was found that the Mg pp′ group (2776 to 2783 A) appears at current densities less than 0.2 milliampere per square centimeter. Since these lines are produced by electron transitions from an initial state in which there are two electrons in virtual orbits, this observation shows that the two electrons are moved to these orbits as a result of a single collision; lines which could be produced only by successive impact are entirely absent at much larger current densities. The pp′ group of Cd (2239 to 2329 A) appears at its quantum voltage, but is too faint to be detected at current densities which exclude the possibility of successive excitation.
Several lines of Cd, In, and Tl are classified by the use of primed terms.
Extension of the subordinate series of Cd: spectra of Cd below the ionization potential. The low-voltage arc in Cd yielded a number of new lines of the singlet and triplet subordinate series. In exposures taken below the ionization potential the lines of Cd are excited exactly at the voltage intervals predictable from the classification of the spectrum.
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