The Dipole Moment of Isocyanic Acid, HNCO, and its Astrophysical Consequences

The component of the dipole moment of D14N12C1 along its b-inertial axis (j ) has been found from measurements of the Stark effect to be 1.35 + 0.t debye. This value, when combined with earlier data, gives a total dipole moment of 2.1 + 0.15 debye. It is shown that the value of for H14N12C16O lies within the quoted error limits of that for D14N12C16O. Thus the microwave emission of the 413-312 rotational transition of H'4N12C'6O in the direction of the galactic radio source Sgr B2 is emitted by rotational levels that have lifetimes for spontaneous emission of only 120 s. If only collisional excitation is considered, the density of H2 molecules in the core of the Sgr B2 cloud must be > 108 . We discuss some further K-type doublet transitions of HNCO, which might be detected in space. Subject heading: molecules, interstellar