The chemiionizaion in hydrogen is measured with the aid of the photodissociation of the H2-molecules. Only the reaction of hydrogen atoms is discussed in this paper. The atoms are produced by the photoabsorption of special wavelengths in the region between the dissociation and ionization limit thereby forming metastable 2S-atoms with a well defined kinetic energy. The energy dependence of the reaction cross section is determined which follows a ν-n -law, where n is found to be between 2 and 3 and ν is the velocity of the atoms.