Quadrupole coupling in alkali metal amides MNH2 (X~1A1): An experimental and computational study

• First experimental determination of the quadrupole coupling in metal amide species. • First FTMmmW measurements (22–58 GHz) of LiNH 2 and NaNH 2 . • Further evidence for strong ionic bonding in alkali amide molecules. • First computed structure for KNH 2 ( X ~ 1 A 1 ) with a modern basis set for future work. Rotational spectra of LiNH 2 and NaNH 2 have been recorded using Fourier transform microwave/millimeter-wave (FTMmmW) techniques in the range 22 – 59 GHz. The species were created from the reaction of metal vapor and ammonia, diluted in argon, using a Discharge-Assisted Laser Ablation Source (DALAS). The J Ka,Kc = 1 01 → 0 00 transition was measured for both molecules, as well as the J Ka,Kc = 2 02 → 1 01 transition for NaNH 2, all of which exhibited quadrupole coupling splittings. The two data sets were each analyzed with an S -reduced asymmetric top Hamiltonian, establishing the lithium and sodium electric quadrupole coupling parameter, χ aa for the first time, and refining previous rotational constants. Quadrupole and nuclear-spin rotation interactions were also computationally investigated at the MP2/6-311G++(3df,2pd) level for LiNH 2 , NaNH 2 and KNH 2 . These calculations suggest that the major contributor to the quadrupole interactions is the alkali metal nucleus, not that of nitrogen, as confirmed experimentally. Comparison of quadrupole coupling constants suggest that LiNH 2 and NaNH 2 are principally ionic molecules with a charge distribution similar to LiF and NaF.