Photodissociative formation of ion pairs from molecular hydrogen and the electron affinity of the hydrogen atom

Abstract

Photodissociative production of ion pairs from H 2 has been observed in the wavelength range 706–718 A at spectral resolution of 0.4 and 0.22 A. From measured thresholds for production of H − from H 2 molecules in each of the three lowest rotational states, the lower bound EA(H) ⩾ 0.754 ± 0.002 eV is obtained, in excellent agreement with the theoretical electron affinity of 0.75421 eV. For formation of D − from D 2, a threshold assigned to molecules in the rotational state J = 2 has been measured, from which the bound EA(D) ⩾ 0.757 ± 0.005 eV is obtained. Negative ion yield curves are presented for hydrogen.