Trends in the alkaline-earth amide series: The millimetre-wave spectrum of MgNH2 and MgND2 (2A1)

Abstract

The pure rotational spectra of MgNH2 ([Formula: see text]2A1) and its deuterium isotopomer have been recorded using millimetre/sub-millimetre wave direct absorption techniques. Both species were synthesized by the reaction of magnesium vapor and either NH3 or ND3 in a dc discharge. Twelve rotational transitions were measured for MgNH2, and eight transitions were observed for MgND2, both in the range 120–530 GHz. Asymmetry components with Ka= 0–5,7, and sometimes 6, were measured for nearly every transition. Rotational, centrifugal distortion, and spin–rotation parameters have been accurately determined for both molecules, as well as an r0 structure for magnesium amide. The data indicate that MgNH2is a planar molecule with C2v symmetry, similar to CaNH2 and SrNH2, and does not undergo inversion. However, there appears to be subtle differences between MgNH2 and its calcium and strontium analogs. Magnesium amide, for example, has a significantly larger H–N–H bond angle than CaNH2and SrNH2. In addition, the spin–rotation constants indicate slightly more in-plane p character for the unpaired electron in this molecule relative to that in calcium or strontium amide. Such differences may result from more covalent character in the bonding of MgNH2 in comparison to the heavier alkaline-earth amide species. PACS No.: 32.20Bx