ABSTRACT. We present high spectral resolution and high-sensitivity observations of the J = 1 → 0 transition of N₂H⁺ 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 N₂H⁺ 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.

Subject headings: ISM: molecules; molecular data

Print publication: Issue 1 (1995 December 10)
Received 1995 July 28, accepted for publication 1995 September 18