Review of atomic physics as applied to the diffuse interstellar medium

Atomic physics processes relevant to the ionisation and thermal balance of the diffuse interstellar medium are reviewed. Particular attention is paid to charge transfer reactions, dielectronic recombination, and to photoionisation and radiative recombination. Collisional excitation of fine structure transitions by electrons and hydrogen atoms is also considered in relation to the cooling of the interstellar gas. (orig.)