  We present a sample of 383 X-ray selected galaxy groups and clusters with
spectroscopic redshift measurements (up to z ~ 0.79) from the 2XMMi/SDSS Galaxy
Cluster Survey. The X-ray cluster candidates were selected as serendipitously
detected sources from the 2XMMi-DR3 catalogue that were located in the
footprint of the Sloan Digital Sky Survey (SDSS-DR7). The cluster galaxies with
available spectroscopic redshifts were selected from the SDSS-DR10. We
developed an algorithm for identifying the cluster candidates that are
associated with spectroscopically targeted luminous red galaxies and for
constraining the cluster spectroscopic redshift. A cross-correlation of the
constructed cluster sample with published optically selected cluster catalogues
yielded 264 systems with available redshifts. The present redshift measurements
are consistent with the published values. The current cluster sample extends
the optically confirmed cluster sample from our cluster survey by 67 objects.
Moreover, it provides spectroscopic confirmation for 78 clusters among our
published cluster sample, which previously had only photometric redshifts. Of
the new cluster sample that comprises 67 systems, 55 objects are newly X-ray
discovered clusters and 52 systems are sources newly discovered as galaxy
clusters in optical and X-ray wavelengths. Based on the measured redshifts and
the fluxes given in the 2XMMi-DR3 catalogue, we estimated the X-ray
luminosities and masses of the cluster sample.
