Stringent upper limits to the solid NH

We obtained near-infrared spectroscopy of the high mass young stellar object W 33A between 1.9–2.5 μm in search of absorption features of circumstellar ices. The 2.27 μm band of $\rm CH_3OH$ is positively identified in the spectrum, its intensity being fully consistent with the column density derived earlier from the methanol bands at 3.54 and 3.91 μm. The 2.21 μm band of solid $\rm NH_3$, on the other hand, was not detected. This shows that the quantity of solid $\rm NH_3$ towards W 33A is at least 3 times lower than earlier estimates based on the $\rm NH_3$ umbrella mode at 9 μm