Quantum dynamics of the dissociation of H2 on Cu(100): dependence of the site-reactivity on initial rovibrational state

We perform six-dimensional (6D) quantum wavepacket calculations for H2 dissociatively adsorbing on Cu(100) from a variety of rovibrational initial states. The calculations are performed on a new potential energy surface (PES), the construction of which is also detailed. Reaction probabilities are in good agreement with experimental findings. Using a new flux analysis method, we calculate the reaction probability density as a function of surface site and collision energy, for a variety of initial states. This approach is used to study the effects of rotation and vibration on reaction at specific surface sites. The results are explained in terms of characteristics of the PES and intrinsically dynamic effects. An important observation is that, even at low collision energies, reaction does not necessarily proceed predominantly in the region of the minimum potential barrier, but can occur almost exclusively at a site with a higher barrier. This suggests that experimental control of initial conditions could be used to selectively induce reaction at particular surface sites. Our predictions for site-reactivity could be tested using contemporary experimental methods: The calculations predict that, for reacting molecules, there will be a dependence of the quadrupole alignment of j on the incident vibrational state, v. This is a direct result of PES topography in the vicinity of the preferred reaction sites of v = 0 and v = 1 molecules. Invoking detailed balance, evidence for this difference in preferred reaction site of v = 0 and 1 molecules could be obtained through associative desorption experiments.     

Synthesis of sulfur-bridged piperazinediones by reaction of 3,6-dibromo-1,4-dimethyl-2,5-piperazinedione with geminal dithiols

The reaction of several geminal dithiols with 3,6-dibromo-1,4-dimethyl-2,5-piperazinedione gave in good yields piperazinedione derivatives substituted at the 3,6-position with a geminal dithiol-bridging group. These sulfur-bridged piperazinediones formally represent derivatives of the 2,4-dithia-6,8-diaza-7,9-dioxobicyclo[3.2.2]nonane ring system. Attempts to transform these sulfur-bridged piperazinediones to 3,6-epidithiopiperazinediones by removal of the bridging group common to the sulfur functionality were unsuccessful. Studies also are reported of addition of thioacetic acid to 3,6-dimethylene-2,5-piperazinedione to give 3,6-diacetylthio-3,6-dimethyl-2,5-piperazinedione. Conversion of the 3,6-diacetylthio derivative to the epithiopiperazinedione ring system yielded a mixture of epimono- and epidithiopiperazinediones.     

Nuclear size dependence of inclusive particle production

The inclusive production of π⁺, π^?, K⁺, K^?, p and $\text{p}$ for protons incident on carbon and tungsten targets was studied at the Internal Target Area of the Fermilab. We assume an A^α dependence for the inclusive cross sections and report here on the variation of α with incident momentum, transverse momentum and particle species.     

Synthesis of des-n-tetramethyltriostin a from C-terminal Z-d-serine tetra-and octadepsipeptide intermediates

Des-N-tetramethyltriostin A (1), a known DNA-intercalation agent, has been synthesized from tetra- and octapeptide intermediates that have Z-d-serine at the C-terminal position. The procedure thus allows the fragment coupling and cyclization reactions leading to the synthesis of the title compound to occur without racemization at the C-terminal amino acid. Esterification of Boc-Val-OH with the p-bromophenacyl ester of Z-d-serine provided didepsipeptide Z-d-Ser(Boc-Val)-OBpa (4). Stepwise addition of the requisite amino acids provided tetradepsipeptide Z-d-Ser[Boc-Ala-Cys(Acm)-Val]-OBpa (6). Fragment coupling of the respective C- and N-deprotected tetradepsipeptides 7 and 8, derived from 6, furnished linear octadepsipeptide 9, which upon cyclization and disulfide formation gave the bicyclic octadepsipeptide 11, a known synthetic precursor to 1. The degree of racemization incurred in the alanine and valine residues of selected depsipeptides was measured and the results compared with those obtained in previous studies. It was concluded that alanine, perhaps because of sequence effects, undergoes a degree of racemization (4–10%) during hydrolysis of tetradepsipeptide 6 and octadepsipeptide 9.     

Quantum superchemistry: dynamical quantum effects in coupled atomic and molecular Bose-Einstein condensates

We show that in certain parameter regimes there is a macroscopic dynamical breakdown of the Gross-Pitaevskii equation. Stochastic field equations for coupled atomic and molecular condensates are derived using the functional positive- P representation. These equations describe the full quantum state of the coupled condensates and include the commonly used Gross-Pitaevskii equation as the noiseless limit. The full quantum theory includes the spontaneous processes which will become significant when the atomic population is low. The experimental signature of the quantum effects will be the time scale of the revival of the atomic population after a near total conversion to the molecular condensate.     

Die quantitative Verfolgung des Sulfurierungsprozesses

Ohne Zusammenfassung     

Random self-affine multifractal Sierpinski sponges in $${\mathbb{R}^d}$$

In this paper we study the Hausdorff and packing dimensions and the Rényi dimensions of random self-affine multifractal Sierpinski sponges in \({\mathbb{R}^{d}}\).     

二茚基钇-铝双金属配合物催化丙烯腈聚合

丙烯腈 (AN)聚合通常采用自由基和阴离子聚合两种 .它们存在催化剂活性低 ,用量大等缺点 .关于丙烯腈的配位聚合研究报道则较少 .最近 ,有报道发现二价稀土化合物可以催化丙烯腈聚合 ,但催化活性较低[1 ,2 ] .本文以二茚基钇 -铝双金属配合物 (C9H7) 2 Y(μ- Et) 2 Al Et2(以下以 Y- Al代表 )为 AN聚合催化剂 ,发现它单独可以催化 AN聚合 .当外加酚钠(Ph ONa)时 ,可以大大提高聚丙烯腈 (PAN)的产率及分子量 .研究了单体浓度、催化剂浓度、温度、时间等对 AN聚合的影响 ,并对其引发机理进行了研究 .Y- Al的合成及聚合方法见文献 [3…