Detection of Interstellar 12C 15N

We report the first detection of the C(N-15) isotopomer in Orion A with the KOSMA 3 m radio telescope on Gornergrat, Switzerland. Using our newly designed SIS receiver, we detected the strongest feature of the hyperfine pattern of the N = 2 - 1 rotational transition at 219.9 GHz. The frequency predictions used for the lowest three electronic ground-state rotational lines and the N = 2 - 1 transition in particular are based on an in-depth estimate of the molecule's rotational, spin-doubling, and magnetic hyperfine constants. The isotopic ratio (N-14)/(N-15) was derived from a comparison of the optically thin hyperfine components of the C(N-14) species with the C(N-15) transitions and found to be 290 +/- 40, in close agreement with values quoted in the literature for other nitrogen-bearing molecules.