  We report VLBA observations of maser emission from the rotationally excited
doublet Pi 1/2, J=1/2 state of OH at 4765 MHz. We made phase-referenced
observations of W3(OH) at both 4765 MHz and 1720 MHz and found emission in
three fields within a about 2000 AU diameter region and verified that in two of
the three fields, 4765 MHz and 1720 MHz emission arise from the same position
to within about 4 mas (about 5 AU diameter emission regions along an
approximately N-S arc with linear extent about 500 AU. In addition, we carried
out phase-referenced observations of 4765 MHz emission from K3-50. We searched
for the 4765 MHz line in W49 (without phase referencing) and W75N
(phase-referenced to the strongest 4765 MHz maser feature in DR21EX); we were
unable to detect these sources with the VLBA. For 2 1/2 years (including the
dates of the VLBA observations), we carried out monitoring observations of 4765
MHz emission with the VLA. Constraints on models for maser emission at 1720 MHz
and 4765 MHz are derived from the observations. These observations are then
briefly compared with existing models.
