When an electron becomes attached to an atom to form a negative ion an amount of energy equal to the electron affinity of the atom plus the relative kinetic energy of the colliding particles must be dissipated. The disposal of this energy depends upon the process of formation of the ion. One process which takes place in molecular gases is the simultaneous dissociation of the molecule and attachment of the electron to one of the products of dissociation, the energy of the electron in excess of the necessary for dissociation together with the electron affinity of the atom being carried away in kinetic form by the products of dissociation. Negative ions are also believed to be formed by the direct attachment of electrons to atoms and molecules without dissociation. In this process it has generally been assumed that the excess energy is radiated, but, although several attempts have been made, it has not been found possible to detect an electron affinity spectrum.