2013ApJ...775..133C

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 B₀= 5481.4333(6) MHz, D₀= 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 B₀= 5481.49(3) MHz and D₀= 3.2(1) KHz, i.e., identical to the laboratory ones. A merged fit to the laboratory and space frequencies provides B₀= 5481.4336(4) MHz and D₀= 2.94(5) KHz. We have derived a column density for HMgNC of (6±2)x10¹¹/cm2. 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.