2015ApJ...814..119H

The N = 1 ← transition of SH⁺(X³Σ^– in its complete fine structure multiplet (J = 0 ← 1, 2 ← 1, and 1 ← 1) has been measured using submillimeter/THz direct absorption spectroscopy in the frequency range near 346-683 GHz. This work is the first direct laboratory measurement of the J = 0 ← 1 and 1 ← 1 spin components. This molecular ion was created in the gas phase from a mixture of H₂ S and argon in an AC discharge. Hyperfine components, arising from the nuclear spin of H (I = 1/2), were resolved in every fine structure multiplet. The data have been analyzed using a Hund's case b_βJ Hamiltonian, resulting in further improvement in the accuracy of the rotational, spin-rotation, spin-spin, and magnetic hyperfine constants for SH⁺ From these new data, frequency predictions have been made for the N = 2 -> 1 and 3 -> 2 transitions, with an estimated uncertainty of less than 1 MHz. These data also confirm the recent detection of the two hyperfine components of the N = 1 -> 0, J = 0 -> 1 transition of S⁺H in the Orion Bar, as well as the J = 1 -> 1 component of this molecular ion near 683 GHz toward Sgr B2.