The excitation, abundance, and distribution of HNCO in Sagittarius B2

Snyder and Buhl (1972) have discovered isocyanic acid (HNCO) in Sgr B2. It is pointed out that HNCO is a particularly interesting interstellar molecule because under certain conditions it can be employed in a study of the far-infrared radiation field of the cloud in which it resides. The present study was mainly conducted with the aim to establish empirically the extent to which HNCO is populated by radiative processes in a source with a measured far-infrared radiation field. It is attempted to deduce the radiation field from the HNCO excitation conditions. Attention is given to an energy-level diagram of HNCO in the ground electronic and vibrational states, the antenna and receiver properties, a table with the observed parameters toward Sagittarius B2, the velocity structure, the HNCO intensity distribution, a summary of the Sgr B2 properties, the population distribution and column density, and the excitation of HNCO.