ROSAT PSPC Observations of the Richest ($R geq 2$) ACO Clusters

We have compiled an X-ray catalog of optically selected rich clusters of galaxies observed by the PSPC during the pointed GO phase of the ROSAT mission. This paper contains a systematic X-ray analysis of 150 clusters with an optical richness classification of $R geq 2$ from the ACO catalog (Abell, Corwin, and Olowin 1989). All clusters were observed within 45 of the optical axis of the telescope during pointed PSPC observations. For each cluster, we calculate: the net 0.5-2.0 keV PSPC count rate (or $4 sigma$ upper limit) in a 1 Mpc radius aperture, 0.5-2.0 keV flux and luminosity, bolometric luminosity, and X-ray centroid. The cluster sample is then used to examine correlations between the X-ray and optical properties of clusters, derive the X-ray luminosity function of clusters with different optical classifications, and obtain a quantitative estimate of contamination (i.e, the fraction of clusters with an optical richness significantly overestimated due to interloping galaxies) in the ACO catalog.