Thermochemistry of the Dimer Lithium Hydride Molecule Li₂H₂(g)

Abstract

A stable molecule Li 2 H 2 has been identified experimentally and its stability determined.The gas species over solutions of hydrogen in liquid lithium were detected by mass spectrometric analysis of the saturated vapor effusing from a Knudsen cell. From the measurements of the gaseous equilibria Li 2 H 2 (g) + Li2(g) = 2Li 2 H(g), Li 2 H 2 (g) + Li(g) = LiH 2 (g) + Li 2 (g), Li 2 H 2 (g) + Li 2 (g) = Li3(g) + LiH 2 (g) andLi 2 H 2 (g) + LiH(g) = Li 2 H(g) + LiH 2 (g), an atomization energy D°O (Li 2 H 2 )= 164.3 ± 10 kcal/ mol and a heat of dimerization ΔH°O = -(52.6 ± 10) kcal/mol was obtained.Much theoretical work has been carried out on the lithium hydride molecule, which has become the workbench of the theoretical chemist CO, Browne 02), and Fraga and Ransil (3) have given the binding energy for the LiH + ion by ab initio calculation; Companion^) has applied the diatomic-in-molecule theory to the LiJA and LiH 2 molecules and predicted the stabilities of these molecules. We have intensively studied the Li-H system by means of Knudsen effusion mass spectrometry, and identified all predicted molecules and ions as cited above(5), and reported the thermochemical properties of these gaseous species (6, 7^, 8).The existence of a stable molecule Li 2 H 2 has not been demonstrated experimentally prior to this investigation, Tyndall and Companion(9) have studied the stability of ^n^2 ^ application of diatomics-in-molecules theory and given following heats of reaction: 0 2LiH( Z ) -> Li H0 ( B, ) AH n = -28.4 kcal/mol 2 2 lg 0 0097-6156/82/0179-0265$05.00/0

Gaseous Metal Hydrides MBeH<sub>3</sub> and M<sub>2</sub>BeH<sub>4</sub> (M = Li, Na): Quantum Chemical Study of Structure, Vibrational Spectra and Thermodynamic Properties

“…[31]. The calculated enthalpy of dimerization for Li 2 H 2 is in agreement within uncertainty limit with the experimental magnitude by Wu et al [32]. …”

Theoretical study of structural and thermodynamic properties of gaseous metal hydrides m2xh4 (m = li, na; x = be, mg)

“…The properties of the tetraatomic species are displayed in Tables 4 and 5 (Chen et al, 2005). The calculated enthalpy of dimerization for Li 2 H 2 is in agreement within uncertainty limit with the experimental magnitude by (Wu et al, 1982). 1159 (0) 1199 (0) 1194 a 955 (0) 1004 (0) 993 a ω 2 (A g ) 515 (0) 526 (0) 524 a 225 (0) 230 (0) 228 a ω 3 (B 1g ) 886 (0) 911 (0) 902 a 636 (0) 697 (0) 690 a ω 4 (B 1u ) 592 (17.6) 607 (18.6) 604 a 444 (19.3) 459 (21.5) 458 a ω 5 (B 2u ) 967 (22.2) 990 (23.9) 985 a 783 (22.8) 832 (25.4) 823 a ω 6 (B 3u ) 1066 (21.7) 1100 (22.3) 109…”