Density Functional Theory Modeling of Reactions of Addition of H2 Molecules to Magnesium Clusters Mg17M Doped with Atoms M of Transition 3d Elements.

Density functional theory calculations of potential energy surface (PES) have been performed for elementary hydrogenation reactions Mg17M + H2 → Mg17MH2 of magnesium clusters Mg17M doped by transition 3d metals (M = Ti-Ni), and for consecutive reactions Mg17Ni + nH2 → Mg17NiH2n of addition of n hydrogen molecules to Ni-doped clusters Mg17Ni and Mg17NiH2. Energetic, geometric, and spectroscopic features of intermediates and transition states along the minimum energy pathway have been found, and their trends were analyzed with dopants changing along the 3d series and with increasing number of atoms H attached to the surface positions of the magnesium backbone.

Initial ionization reaction in matrix-assisted laser desorption/ionization.

The initial ionization reaction in matrix-assisted laser desorption/ionization (MALDI) was examined on the basis of the appearance of photoelectrons. The threshold laser fluence for the ejection of photoelectrons from 2,5-dihydroxybenzoic acid (DHB), sinapinic acid (SA), and trihydroxyacetopheone (THAP) on stainless steel (SS) substrates was 0.05, 0.41, and 8.39 mJ/cm(2), respectively. These values are considerably lower than those for MALDI ions, indicating that the electron detachment likely precedes other ionization reactions. The SS substrate played an insignificant role in the production of photoelectrons because suspended DHB produced a photoelectron signal similar to DHB on the SS surface, and decreasing the DHB thickness on the SS reduced the photoelectron intensity. For crystalline DHB and SA, the photoelectron intensity increased with the laser (337 nm) fluence in a relationship of less than second order, suggesting considerable reductions of ionization potentials in comparison with free molecules. According to ab initio calculations, the ionization potential of DHB clusters reduces as the cluster size increases from monomer to octamer. The impact of these abundant electrons on the ion production in MALDI is discussed.

A theoretical study of isomerism in doped aluminum MAl12 and MAl12X12 clusters with 40 and 50 valence electrons.

Systematic density functional B3LYP calculations with the 6-31G* and 6-311+G* basis sets have been employed in order to investigate the structure, vibrational frequencies, relative energies, vertical ionization potentials, and magnetic shielding constants of endohedral and exohedral isomers in two related families of doped aluminum MAl12 and alane MAl12H12 clusters with 40 and 50 valence electrons, respectively. Isomerization barriers have been also determined. Trends in these properties with changing heteroatom M in various series have been followed. The similarities and differences between the aluminides and alanes as well as between the alanes MAl12H12 and related boranes MB12H12 and gallanes MGa12H12 have been scrutinized.