Determination of the hyperfine structure of N-2 D+

We present new high spectral resolution observations of the N2D+ J = 2 --> 1 and J = 3 --> 2 as well as N2H+ J = 3 --> 2 lines toward dense molecular cores. The hyperfine structure of the N2H+ and N2D+ transitions is clearly resolved in these sources, in excellent agreement with quantum mechanical c alculations. Optical depths are determined from the observed spectra, leadi ng to D/H values on the order of 10%-30% for the N2D+/N2H+ system. There ar e a large number of hyperfine components, and in addition to providing sate llites, they contribute to the broadening and asymmetric shapes of the N2H and N2D+ line profiles. It is therefore important to take into account the detailed hyperfine structure of the transitions when deducing astrophysica l parameters from observed data.