HNCO in molecular clouds

In a survey of 18 molecular clouds, HNCO JK-1K1 → JarcminKarcmin-1Karcmin1 = 505 → 404 and 404 → 303 emission was detected in seven clouds, and possibly in one other. Emission in these transitions originates in high-density regions (n ⪆ 106 cm-3). The molecule's excitation requirements are used to derive limits to excitation temperatures and optical depths. The possibility of clumping with respect to the beam is discussed. The HNCO emission from Sgr A is an order of magnitude larger than the other detected sources. HNCO is probably a constituent of most molecular clouds.