Metal-insulator segregation in lithium rich LinHm + clusters

Unimolecular and collision-induced dissociation of singly-charged mono-bromide silver clusters Ag(x)Br(+) (x = 2, 4, 6, 8, 10)

Relative intensities of singly-charged mono-bromide silver clusters Ag(x)Br(+) formed from sputtering of a pressed pellet of silver bromide were measured by mass spectrometry. The obtained results suggest that the Ag(x)Br(+) clusters have a structural formula of the form Ag(x-1)(+)(AgBr). The relative stability of Ag(x-1)(+)(AgBr) was determined by the intrinsic stability of the remaining metallic portion of the cluster (Ag(x-1)(+)) as predicted by the spherical jellium model (SJM). Unimolecular and high- energy collision-induced dissociation (CID) spectra of Ag(x)Br(+) (x = 2, 4, 6, 8, 10) clusters were also measured. In all of the spectra, the most intense fragment peaks were assigned to the Ag(x-1)(+) ions accompanying the loss of AgBr. The difference in the relative intensities of the Ag(x-1)(+) peaks between unimolecular dissociation and CID spectra led us to conclude that the weakest bond in the excited cluster Ag(x)Br(+*) is the Ag(x-1)(+)-AgBr bond and the structure of Ag(x)Br(+) is a metallic Ag(x-1)(+) ion cluster adduct with AgBr. The primary fragments observed in the CID spectra were also explained by the stabilities of the generated ion products and neutral fragments, both having even delocalized valence electrons. The present results were consistently explained by SJM. The dissociation behavior of Ag(2)Br(+) can be explained on the basis of the calculated thermochemical data.

Theoretical Study on the Small Clusters of LiH, NaH, BeH2, and MgH2

High-level ab initio molecular orbital theory is used to calculate the geometries, vibrational frequencies, atomic charges, and binding energies of the small clusters (LiH)(n), (NaH)(n), (BeH(2))(n), and (MgH(2))(n) (n = 1-4). For (LiH)(n) and (NaH)(n), there are planar cyclic structures when n = 2, 3. We have found the cubic structure T(d) in addition to the planar cyclic D(4)(h) when n = 4. The D(4)(h) is less stable than the T(d) geometry. For (BeH(2))(n) and (MgH(2))(n), when n = 3, there are three kinds of structures: chain C(2)(v), planar cyclic D(3)(h), and hat-like C(2)(v). The C(2)(v) geometry is more stable than the others. When n = 4, there are four kinds of structures: chain D(2)(h), cubic T(d), string-like C(2), and cubic transformation C(1). The most stable compounds in the families of (LiH)(n), (NaH)(n), (BeH(2))(n), and (MgH(2))(n) are cubic T(d), cubic T(d), chain D(2)(h), and string-like C(2) geometries, respectively, when n = 4. Calculated binding energies range from -24 to -37 kcal/mol for (LiH)(n) and --19 to -30 kcal/mol for (NaH)(n), (BeH(2))(n), and (MgH(2))(n). The hydrogen atoms in hydride clusters always have negative charges. The atomic charges of planar cyclic structures are weaker than those of cubic structures, and there is a tendency of reducing along with the increase of the cluster size. The vibrational frequencies of planar cyclic structures have consistent tendency, too. It indicates that the bond distance increases with the ionic character of the bond.

Stability and structure of LinH molecules (n=3–6): Experimental and density functional study

The molecules Li(3)H and Li(4)H have been identified in mass-spectrometric measurements over solutions of hydrogen in liquid Li, and the gaseous equilibria of the reactions: Li(3)H+Li=Li(2)H+Li(2), Li(3)H+Li(2)=Li(2)H+Li(3), Li(3)H+Li=LiH+Li(3), Li(3)H+LiH=2Li(2)H, and Li(4)H+Li(2)=Li(3)H+Li(3) have been measured. Density functional calculations of Li(n)H molecules (n=3-6) provide structures, vibrational frequencies, ionization energies, and free energy functions of these molecules, and these are used to estimate the enthalpies of these reactions and the atomization energies of Li(3)H (119.4 kcal/mol) and Li(4)H (151.8 kcal/mol).