Rifki Muhida

Surface science-based reaction design: increasing the ortho-para hydrogen conversion yield via molecular orientation, a case study

Abstract One of the ultimate goals of surface science is to be able to design and control reactions as they progress on surfaces. This entails an atomic-level understanding of the fundamental principles (elementary processes) underlying the bond-making and bond-breaking at surfaces. Our current understanding has gained significantly from systematic experimental and theoretical studies on such benchmark systems as the interaction of hydrogen with metal surfaces. Yet, fundamental, examples of surface science-based reaction design are extremely few. Here, we consider the ortho – para ( o – p ) H 2 conversion as a case study. We invoke two processes derived from fundamental, surface science insights, based on the effect of molecular orientation on the hydrogen-solid surface reaction, viz., dynamical quantum filtering (DQF) and Steering , and apply them to enhance the o – p H 2 conversion yield/rate. The orientation dependence of the o – p H 2 conversion ( steric effect , SE) dictates that cartwheel-like rotating (CLR) H 2 will have a higher rate of conversion than helicopter-like rotating (HLR) H 2 . Applying DQF, we can then prepare rotationally aligned H 2 , doing either HLR or CLR. This enables us to increase the o – p H 2 conversion yield.

Molecular orientation dependence of o-p H2 conversion on a 3d impurity sitting on a metal oxide surface

We investigate the molecular orientation dependence of the (o)rtho-(p)ara conversion of H 2 interacting with a solid surface. As a first step, we consider the interaction of a H 2 and a 3d impurity on a metal oxide surface. Taking the H 2 -surface electron exchange interaction (Coulomb interaction) and Fermis contact interaction (intra-molecular hyperfine contact interaction) as perturbations, our calculation results indicate that the o-p H 2 conversion yield strongly depends on the H 2 -surface distance and the H-H bond orientation with respect to the surface normal.

Molecular Orientation Dependence of o–p Conversion of H2 Scattered from a 3d Impurity Sitting on a Metal Oxide Surface

We investigate the dynamics of o – p conversion of H 2 scattered from a 3 d impurity sitting on a metal oxide surface. We treat Fermis contact interaction (intra-molecular hyperfine contact interaction) and the H 2 -surface electron exchange interaction (Coulomb interaction) as perturbations. Numerically, we calculate the o – p H 2 conversion yield as functions of the H–H bond orientation with respect to the surface normal and translational energy of H 2 . We find that the o – p H 2 conversion yield decreases exponentially with increasing translational energy, and strongly depends on the H–H bond orientation with respect to the surface normal. The o – p H 2 conversion yield shows that a perpendicular orientation is preferred over a parallel orientation.

Molecular orientation dependence of ortho-para conversion of a H2 interacting with a metal surface

In order to obtain a general conclusion regarding the steric effect on the ortho-para H2 (o-p H2) conversion on solid surfaces, we investigate the molecular orientation dependence of the o-p conversion of a H2 interacting with a metal surface. Taking the H2-surface electron interaction (Coulomb interaction) and Fermi’s contact interaction as perturbations, our calculation results indicate that the o-p H2 conversion yield for a H2 oriented perpendicular to the surface is larger than that for a H2 oriented parallel to the surface. These results and the conclusion thus obtained generalize the steric effect on the o-p H2 conversion on metal oxide surfaces obtained previously.

Spin polarization of a multiple-decked sandwich clusters: M(C6H6)2 (M = Mn, Fe, Co)

We investigate the spin polarization of a multiple-decked sandwich cluster, viz ., M n (C 6 H 6 ) n +1 . As a first step, we consider M n (C 6 H 6 ) n +1 clusters with n =1 and M = Mn, Fe, Co. Based on the density functional theory, we find an increase in the magnetic moment of the benzene clusters, and a decrease in the magnetic moment of M in the M(C 6 H 6 ) 2 systems. From increased magnetic moment of benzenes, we find a way to inject spin to benzenes through 2 p z orbitals.

Change of magnetic properties of benzenes in multiple-decked sandwich clusters: Mnn(C6H6)n+1 (n = 1, 2)

Local magnetic moments in benzenes of a multiple-decked sandwich cluster, namely, Mnn(C6H6)n+1 (n = 1,2) are investigated using density functional theory. A significant increase in the magnetic moments of benzenes was found in the 2pz orbitals. From the values of the local magnetic moments of Mn(C6H6)2 and Mn2(C6H6)3, we find that the local magnetic moment of benzene in the centre of the chain is larger than that at the edge position. These results indicate a promising possibility of changing the magnetic properties of benzenes using a magnetic material.

First-Principles Calculations for Chemical Reaction between Sodium Diethyldithiocarbamate and Transition-Metal (Cr) atom to Produce Cr(DDC)3 and Cr(DDC)2ODDC

We investigate the chemical reaction between a Cr transition-metal atom and sodium diethyldithiocarbamate (NaDDC), a complexing agent used to detect and extract Cr in human blood samples. Using density-functional-theory-based calculations, we determine their stable structures of Cr(DDC)2ODDC and Cr(DDC)3 complexes and obtain their dissociation energies. We found dissociation energies of -10.66 and -3.24 eV for Cr(DDC)2ODDC and Cr(DDC)3 complexes, respectively. Hence, on the basis of dissociation energies, we have verified that the reaction of NaDDC with Cr produces Cr(DDC)2ODDC as a major product.

Steric effect on o-p conversion of a H2 interacting with a 3d impurity sitting on a metal oxide surface

Steric effect on the o-p conversion of a H 2 interacting with a 3d impurity sitting on a metal oxide surface is investigated by comparing the o-p conversion yield/rate for a H 2 doing cartwheel-like rotation (i.e., the rotational axis of H 2 is parallel to the surface) with that for a H 2 doing helicopter-like rotation (i.e., the rotational axis of H 2 is perpendicular to the surface). The yield of o-p H 2 conversion is calculated by using the perturbation theory, where Fermis contact interaction (intra-molecular hyperfine contact interaction) and the H 2 -surface electron exchange interaction (Coulomb interaction) represent the perturbation terms. On the basis of the calculated results, for the transition from the lowest rotational state of an ortho H 2 (with rotational quantum number j = 1) to the lowest rotational state of a para H 2 (j = 0), the o-p H 2 conversion yield shows that for a H 2 doing cartwheel-like rotation is higher than that for a H 2 doing helicopter-like rotation.

First Principles Study of Electric and Magnetic Properties of Benzene–Iron Multiple-Decked Sandwich Chain

We investigate electric and magnetic properties of a benzene–iron multiple-decked sandwich chain [Fe(C 6 H 6 )] ∞ . By performing first principles calculation based on the density functional theory, we find that the system [Fe(C 6 H 6 )] ∞ is stable and has no magnetic moment for which the two succeeding iron atoms are antiferromagnetically arranged. We propose a superexchange interaction mechanism for this antiferromagnetic order.

Magnetic-Adsorbate-Induced Spin Polarization in Carbon Materials-Two Fe Atoms on Planar C10 and C10H8-

Here we consider a nanoscale material consisting of two Fe atoms sitting on a planar C 10 cluster. On the basis of the density functional theory (DFT), we demonstrate how it is feasible to induce s...