Surface layer relaxation on Mo(111) measured by low energy alkali ion scattering

The surface of clean Mo(111) has been studied using Li⁺ ion scattering at 1000 eV. The dependence of single scattering intensity was measured as a function of incident polar angle in the [12̄1] and the [21̄1̄] azimuths for various total scattering angles. Very pronounced intensity cut-offs are observed and are readily assignable to shadowing and blocking effects in scattering from first, second or third layer atoms. After taking certain precautions to avoid interference from deeper layers, the measured positions of the features yield the first-second layer spacing which is found to be strongly contracted by (18 ± 2)% compared to the bulk spacing. The method also indicates that the second-third layer spacing is possibly expanded (4 ± 4)%, but this result is uncertain due to possible contributions from deeper layers which make this value an upper limit of the layer spacing. The physical implications of these results and the uncertainties in the technique are discussed.     

The multilayer melting transition in methane adsorbed on graphite

High resolution heat capacity measurements of multilayer methane adsorbed on graphite are presented and analyzed. The evidence indicates the presence of two wetting transitions: a first-order dewetting transition at T_w = 90.48 K, and a continuous wetting transition at the triple point, T_t = 90.66 K. This behavior is to be expected in connection with the melting transition in any system where both solid and liquid wet the surface. Heat capacity measurements can provide a valuable diagnostic tool for the wetting behavior of films too thick to be investigated by other means. In the thin film limit, we find that the latent heat of melting vanishes at about 4 layers.     

The effect of dimer mobility on thin film nucleation kinetics

Dimer mobility and dissociation energies of small clusters have been incorporated into a set of rate equations to study the extent of the cluster mobility effect on thin film nucleation kinetics. The numerical analysis results showed that total cluster density and condensation coefficient both increase with increasing dimer dissociation energy and decrease with increasing dimer mobility. By comparison of theoretical calculations with the experimental results of Velfe et al. for Au deposition on NaCl [Thin Solid Films 98 (1982) 15], it is suggested that for this system at 150°C the dimer dissociation energy is low and dimer mobility has little effect on the nucleation kinetics.     

Darstellung und NMR-spektroskopische charakterisierung einiger di-n-alkyl- und n-alkylaryl-chlorphosphane

A series of di-n-alkyl and n-alkylaryl chlorophosphines has been prepared by the reaction of tetraorganodiphosphines with chlorodiphenyl or dichlorophenyl phosphine and characterized by ³¹P and ¹³C NMR spectra.     

Trihydridoruthenium(IV) complexes: preparation and photo-induced H/D exchange reaction

The trihydrides (η⁵-C₅Me₅RuH₃(PR₃ = PMe₃, FEt₃, Pipr₃, PCy₃, PPh₂Me, and PPh₃) (2) are formed in the reaction of paramagnetic (η⁵C₅Me₅)RuCl₂(PR₃) (1) with NaBH₄ in ethanol. The reaction of 1 with NaBH₄, in THF yields intermediary tetrahydroborate complexes (η⁵-C₅Me₅)Ru(PR₃)(BH₄) (3), which are converted to the trihydrides 2 by treatment with ethanol. Irradiation of 2c and 2f in C₆D₆ solution with UV light causes H/D exchange reaction among the solvent, hydride ligands, and the coordinated phosphine.     

Facile access to methyl tantalum derivatives by unprecedented phosphorus—methyl bond cleavage of dimethylphenylphosphane

Reactions of the paramagnetic pentacoordinated TaBr₃(PhPMe₂)₂ adduct with strong bases, (RLi (R = Me, Bu) or 1,8-bis(dimethylamino)naphthalene) have been found to give methyltantalum(IV) derivatives as a result of PMe bond cleavage.     

Organoborierung von alkinylstannanen: XVI. borol-synthese über die organoborierung von BIS(alknyl)Boranen

The organoboration of a new alkynylborane, diethylamino-bis(trimethylstannyl-ethynyl)borane gives 1-diethylamino-2,5-bis(trimethylstannyl)-3-diethylboryl-4-ethtylborol and 1-diethylamino-2-diethylboryl-3,5-bis(trimethylstannyl)-4-ethylborol. The stepwise reaction progress was monitored by NMR spectrocopy (¹H, ¹¹B, ¹³C, ¹¹⁹Sn) and the results were compared with those of the organoboration of bis(diethylamino)-trimethylstannylethynylborane.     

5-germaspiro[4.4]nona-2,7-dienes

A novel series of bicyclic organogermanium derivatives: 5-germaspiro[4.4]nona-2,7-dienes have been prepared by reaction of 1,1-dihalogermacyclopent-3-enes with the appropriate conjugated diene and an alkali metal in a suitable organic solvent. The best results were obtained by using 1,1-dichlorogermacyclopentenes with isoprene or 2,3-dimethylbutadiene and lithium in 5/1 ether/tetrahydrofuran. Except for 2,3,7,8-tetramethyl-5-germaspiro[4.4]nona-2,7-diene, which is crystalline, the 5-germaspirononadienes are colourless liquids, which distil without decomposition under reduced pressure but which slowly polymerize on standing. In the mass spectra of all the spiradienes, the main peak corresponds to the loss of one ring, the less substituted in the case of unsymmetrical molecules. Attempts to obtain 5-germaspiro[4.4]nona-2,7-diene were unsuccessful.