Laboratory and Astronomical Discovery of Hydromagnesium Isocyanide

We report on the detection of hydromagnesium isocyanide, HMgNC, in the laboratory and in the carbon-rich evolved star IRC+10216. The J = 1–0 and J = 2–1 lines were observed in our microwave laboratory equipment in Valladolid with a spectral accuracy of 3 KHz. The hyperfine structure produced by the nitrogen atom was resolved for both transitions. The derived rotational constants from the laboratory data are B 0 = 5481.4333(6) MHz, D 0 = 2.90(8) KHz, and eQq( N ) = −2.200(2) MHz. The predicted frequencies for the rotational transitions of HMgNC in the millimeter domain have an accuracy of 0.2–0.7 MHz. Four rotational lines of this species, J = 8–7, J = 10–9, J = 12–11, and J = 13–12, have been detected toward IRC+10216. The differences between observed and calculated frequencies are <0.5 MHz. The rotational constants derived from space frequencies are B 0 = 5481.49(3) MHz and D 0 = 3.2(1) KHz, i.e., identical to the laboratory ones. A merged fit to the laboratory and space frequencies provides B 0 = 5481.4336(4) MHz and D 0 = 2.94(5) KHz. We have derived a column density for HMgNC of (6 ± 2) × 10 11 cm −2 . From the observed line profiles the molecules have to be produced in the layer where other metal-isocyanides have been already found in this source. The abundance ratio between MgNC and its hydrogenated variety, HMgNC, is ≃20.