We present new measurements of the growth rates of faceted ice crystals in the temperature range -40 < T < -2 degrees C, from which we infer the surface attachment coefficients for the two principal facets. Our data are well described by a polynucleation model, allowing a determination of the molecular step energy as a function of temperature for both facets. These results are a substantial improvement over previous work, and we present an analysis showing that the inconsistencies seen in prior measurements could be explained by systematic errors associated with diffusion effects and substrate interactions. These data provide new insights into the surface attachment kinetics governing ice crystal growth, and they suggest new avenues for examining ice growth behavior using molecular dynamics simulations. Knowledge gained by a detailed case study of ice may in turn lead to a greater general understanding of the fundamental physics underlying crystal growth dynamics. (C) 2013 Elsevier B.V. All rights reserved.