Electric dipole radiation from spinning dust grains

We discuss the rotational excitation of small interstellar grains and the r esulting electric dipole radiation from spinning dust. Attention is given t o excitation and damping of grain rotation by collisions with neutrals, col lisions with ions, "plasma drag," emission of infrared radiation, emission of electric dipole radiation, photoelectric emission, and formation of H-2 on the grain surface. Electrostatic "focusing" can substantially enhance th e rate of rotational excitation of grains colliding with ions. Under some c onditions, "plasma drag"-due to interaction of the electric dipole moment o f the grain with the electric field produced by passing ions-dominates both rotational damping and rotational excitation. Emissivities are estimated f or dust in different phases of the interstellar medium, including diffuse H I clouds, warm H I, low-density photoionized gas, and cold molecular gas. Spinning dust grains could explain much, and perhaps all, of the 14-50 GHz background component recently observed by Kogut et al., de Oliveira-Costa e t al., and Leitch et aI. Future sensitive measurements of angular structure in the microwave sky brightness from the ground and from space should dete ct this emission from high-latitude H I clouds. It should be possible to de tect rotational emission from small grains by groundbased pointed observati ons of molecular clouds, unless these grains are less abundant there than i s currently believed.