  We use ROSAT All Sky Survey (RASS) broadband X-ray images and the optical
clusters identified from SDSS DR7 to estimate the X-ray luminosities around
$\sim 65,000$ candidate clusters with masses $\ga 10^{13}\msunh$ based on an
Optical to X-ray (OTX) code we develop. We obtain a catalogue with X-ray
luminosity for each cluster. This catalog contains 817 clusters (473 at
redshift $z\le 0.12$) with $S/N> 3$ in X-ray detection. We find about $65\%$ of
these X-ray clusters have their most massive member located near the X-ray flux
peak; for the rest $35\%$, the most massive galaxy is separated from the X-ray
peak, with the separation following a distribution expected from a NFW profile.
We investigate a number of correlations between the optical and X-ray
properties of these X-ray clusters, and find that: the cluster X-ray luminosity
is correlated with the stellar mass (luminosity) of the clusters, as well as
with the stellar mass (luminosity) of the central galaxy and the mass of the
halo, but the scatter in these correlations is large. Comparing the properties
of X-ray clusters of similar halo masses but having different X-ray
luminosities, we find that massive halos with masses $\ga 10^{14}\msunh$
contain a larger fraction of red satellite galaxies when they are brighter in
X-ray. ... A cluster catalog containing the optical properties of member
galaxies and the X-ray luminosity is available at {\it
http://gax.shao.ac.cn/data/Group.html}.
