Determination of the Hyperfine Structure of N[TINF]2[/TINF]D[TSUP]+[/TSUP]

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Abstract
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 calculations. Optical depths are determined from the observed spectra, leading to D/H values on the order of 10%-30% for the N2D+/N2H+ system. There are a large number of hyperfine components, and in addition to providing satellites, 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 astrophysical parameters from observed data.