Excited Atoms. Attention is called to the accumulating evidence that normal atoms and those which are “excited” by the displacement of an electron to an outer orbit may have very different physical, chemical, and spectroscopic properties. Thus all atoms, even the inert atoms like helium, are electronegative when excited and tend to form homopolar and heteropolar compounds and negative ions. These compounds and ions are often sufficiently stable to exist for some time in a discharge tube. In any case they profoundly affect the spectrum of the substance.
Reversible Effects of Impacts. Klein and Rosseland point out reasons for believing that an excited atom may revert to the normal state by transferring its energy to a free electron at a collision as well as by radiation. Franck points out that such radiationless transfers of energy may also occur at a collision between an excited and a normal atom.
Phenomena due to Radiationless Transfers of Energy. Franck and Cario show that such transfers of energy may account for (1) the quenching of fluorescence by foreign gases, (2) the excitation of the spectrum of one metal vapor by resonance radiation of another vapor which is mixed with it, (3) the dissociation of hydrogen by mercury 2536 A radiation when mercury vapor is mixed with the hydrogen. These suggestions are critically reviewed.
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