Radio-astronomical Spectroscopy of the Hyperfine Structure of N[TINF]2[/TINF]H[TSUP]+[/TSUP]

We present high spectral resolution and high-sensitivity observations of the J = 1 → 0 transition of N 2 H + at 93 GHz toward the quiescent low-mass cloud core L1512 in Taurus. The relative frequencies of the seven hyperfine components of this transition have been determined with precision ~1 kHz, and the absolute frequencies with precision ~7 kHz. The hyperfine coupling constants have been determined with precision an order of magnitude higher than previously in the laboratory. Relative intensities of the hyperfine components of N 2 H + in L1512 as well as in a sample of ~60 low-mass cloud cores are not consistent with a single excitation temperature model fit, indicating the presence of excitation anomalies.