RADIO-ASTRONOMICAL SPECTROSCOPY OF THE HYPERFINE-STRUCTURE OF N2H+

We present high spectral resolution and high-sensitivity observations of the J = 1 --> 0 transition of N2H+ at 93 GHz toward the quiescent l ow-mass cloud core L1512 in Taurus. The relative frequencies of the se ven hyperfine components of this transition have been determined with precision similar to 1 kHz, and the absolute frequencies with precisio n similar to 7 kHz The hyperfine coupling constants have been determin ed with precision an order of magnitude higher than previously in the laboratory. Relative intensities of the hyperfine components of N2H+ i n L1512 as well as in a sample of similar to 60 low-mass cloud cores a re not consistent with a single excitation temperature model fit, indi cating the presence of excitation anomalies.