Photoelectron yield enhancement of small graphite and silicate dust grains.

Abstract

The photoelectron yield for small grains can be much larger than the bulk values, due to the large surface to volume ratio, which leads to an increase in the probability of escape of a photoelectron. Emission of photoelectrons from small interstellar dust grains is believed to be a significant source of heating of interstellar gas. The heating rate is sensitive to the photoelectric yield of the proposed dust grains. A model based on the Mie solution to the vector electromagnetic wave equation in the presence of a sphere is adopted. Unlike the traditional Mie scattering problem, the electromagnetic fields inside the sphere are considered. Previous calculations utilizing the model are extended. In particular, the relationship of the relative photoelectron yield to wavelength and grain size via a complex index of refraction is investigated. Graphite and silicate grains are considered because they are possible components of interstellar dusts. The published values of absolute photoelectric yield for bulk samples are then used to calculate the absolute yield of small dust grains. The use of exp(i∞t) and exp(-i∞t) time-conventions in this problem are compared.