High-mass star-forming cloud G0.38+0.04 in the Galactic Center Dust
  Ridge contains H2CO and SiO masers
  We have discovered a new H$_2$CO (formaldehyde) $1_{1,0}-1_{1,1}$ 4.82966 GHz
maser in Galactic Center Cloud C, G0.38+0.04. At the time of acceptance, this
is the eighth region containing an H$_2$CO maser detected in the Galaxy. Cloud
C is one of only two sites of confirmed high-mass star formation along the
Galactic Center Ridge, affirming that H$_2$CO masers are exclusively associated
with high-mass star formation. This discovery led us to search for other
masers, among which we found new SiO vibrationally excited masers, making this
the fourth star-forming region in the Galaxy to exhibit SiO maser emission.
Cloud C is also a known source of CH$_3$OH Class-II and OH maser emission.
There are now two known SiO and H$_2$CO maser containing regions in the CMZ,
compared to two and six respectively in the Galactic disk, while there is a
relative dearth of H$_2$O and CH$_3$OH Class-II masers in the CMZ. SiO and
H$_2$CO masers may be preferentially excited in the CMZ, perhaps due to higher
gas-phase abundances from grain destruction and heating, or alternatively
H$_2$O and CH$_3$OH maser formation may be suppressed in the CMZ. In any case,
Cloud C is a new testing ground for understanding maser excitation conditions.
