IR characterizations of lithium imide and amide

Li2NH was synthesized by decomposing of LiNH2 at 673 K under vacuum. Li2NH absorbed and desorbed 6.0-7.0 wt.% of hydrogen at 573-673 K in the pressure range of 9-0.001 MPa. According to the van't Hoff equation, the standard enthalpy change of the hydride reaction was about -66 kJ/mol H2. The hydrogen absorption and desorption by Li2NH was characterized by infrared spectroscopy. We found that IR bands at 3260 cm-1 and 3315 cm-1 of LiNH2 shift to 3180 cm-1 and 3250 cm-1 in the infrared spectrum of Li2NH. The broad IR bands shapes of the hydrogenated specimen (LiNH2) were related with the smaller crystallite size and/or the increasing crystallite disorder