Evidence for weak maser action in interstellar cyanodiacetylene

The J=1..-->..0 and J=8..-->..7 rotational transitions of interstellar cyanodiacetylene have been observed in Sgr B2. These observations confirm the earlier detection of this heavy molecule, and provide further information on its excitation. The J=8..-->..7 line and the previously observed J=4..-->..3 line can be fitted to a thermal equilibrium model and give a total column density of 1.5 x 10/sup 14/ cm/sup -2/. The J=1..-->..0 transition is much stronger than expected from thermal equilibrium, and suggests maser action. (AIP)