  Radiative torques, due to the absorption and scattering of starlight, are
thought to play a major role in the alignment of grains with the interstellar
magnetic field. The absorption of radiation also gives rise to recoil torques,
associated with the photoelectric effect and photodesorption. The recoil
torques are much more difficult to model and compute than the direct radiative
torque. Here, we consider the relatively simple case of a spheroidal grain.
Given our best estimates for the photoelectric yield and other relevant grain
physical properties, we find that the recoil torques contribute at the 10%
level or less compared with the direct radiative torque. We recommend that the
recoil torques not be included in models of radiation-driven grain alignment at
this time. However, additional experimental characterization of the surface
properties and photoelectric yield for sub-micron grains is needed to better
quantify the magnitude of these torques.
