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Green, S., J.A. Montgomery, Jr., and P. Thaddeus, 1974: Tentative identification of U93.174 as the molecular ion N2H+. Astrophys. J., 193, L89-L91.
On the basis of a self-consistent field calculation of its rotation constant and hyperfine structure, it is suggested that the molecular ion N2H+ is the carrier of the unidentified interstellar triplet reported by Turner in the preceding Letter. The calculated frequency of the J=0-1 transition of N2H+ is 92.2 ± 1.8 GHz, in good agreement with the observed 93.1 GHz. Similarly, the calculated value of the quadrupole coupling constant for the outer nitrogen is -5.3 ± 0.5 MHz, while the coupling constant deduced from observations is -5.7 MHz. Equally important to the assignment, the quadrupole coupling for the inner nitrogen is calculated to be only -1.2 ± 0.5 MHz, making its contribution to the hyperfine structure too small to be resolved in the sources so far observed. Detection of additional structure in sources with very narrow lines would provide additional confirmation of the assignment.
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