Georg Ch. Mellau

Heterogeneous oxidation catalysis on ruthenium: bridging the pressure and materials gaps and beyond

It is shown that both the materials and the pressure gaps can be bridged for ruthenium in heterogeneous oxidation catalysis using the oxidation of carbon monoxide as a model reaction. Polycrystalline catalysts, such as supported Ru catalysts and micrometer-sized Ru powder, were compared to single-crystalline ultrathin RuO2 films serving as model catalysts. The microscopic reaction steps on RuO2 were identified by a combined experimental and theoretical approach applying density functional theory. Steady-state CO oxidation and transient kinetic experiments such as temperature-programmed desorption were performed with polycrystalline catalysts and single-crystal surfaces and analyzed on the basis of a microkinetic model. Infrared spectroscopy turned out to be a valuable tool allowing us to identify adsorption sites and adsorbed species under reaction conditions both for practical catalysts and for the model catalyst over a wide temperature and pressure range. The close interplay of the experimental and theoretical surface science approach with the kinetic and spectroscopic research on catalysts applied in plug–flow reactors provides a synergistic strategy for improving the performance of Ru-based catalysts. The most active and stable state was identified with an ultrathin RuO2 shell coating a metallic Ru core. The microscopic processes causing the structural deactivation of Ru-based catalysts while oxidizing CO have been identified.

Long-term stability of Ru-based protection layers in extreme ultraviolet lithography: A surface science approach

Extreme ultraviolet lithography (EUVL) is a leading candidate for next-generation lithography for the semiconductor industry. This technology uses EUV light with a wavelength of 13.5nm (92.5eV) to be able to produce features as small as 20nm in size. The short wavelength of EUV means that reflective optics is needed for lithography in the form of Si–Mo multilayer stacks. However, surface contamination by water and hydrocarbons together with EUV light reduces unacceptably the mirror reflectivity with time. In this article, the authors review the material properties of two promising capping layer materials, Ru and RuO2, for protecting the EUVL mirrors against oxidation, carbon uptake, and the permeation of hydrogen and oxygen. Special emphasis is put on the surface properties of these potential cap layer systems. For both materials the microstructure, the morphology, and the stability under oxidizing and reducing environments are reviewed to promote the search for a successful candidate for a capping layer ...

Complete experimental rovibrational eigenenergies of HCN up to 6880 cm−1 above the ground state

The [H,C,N] molecular system is a very important model system to many fields of chemical physics and the experimental characterization of highly excited vibrational states of this molecular system is of special interest. This paper reports the experimental characterization of all 3822 eigenenergies up to 6880 cm(-1) relative to the ground state in the HCN part of the potential surface using high temperature hot gas emission spectroscopy. The spectroscopic constants for the first 71 vibrational states including highly excited bending vibrations up to v(2) = 10 are reported. The perturbed eigenenergies for all 20 rotational perturbations in the reported eigenenergy range have been determined. The 11,070 eigenenergies up to J = 90 for the first 123 vibrational substates are included as supplement to this paper. We show that a complete ab initio rovibrational analysis for a polyatomic molecule is possible. Using such an analysis we can understand the molecular physics behind the Schrödinger equation for problems for which perturbation theoretical calculations are no more valid. We show that the vibrational structure of the linear HCN molecule persists approximately up to the isomerization barrier and only above the barrier the accommodation of the vibrational states to the double well structure of the potential takes place.

Rovibrational eigenenergy structure of the [H,C,N] molecular system

The vibrational-rotational eigenenergy structure of the [H,N,C] molecular system is one of the key features needed for a quantum mechanical understanding of the HCN⇌HNC model reaction. The rotationless vibrational structure corresponding to the multidimensional double well potential energy surface is well established. The rotational structure of the bending vibrational states up to the isomerisation barrier is still unknown. In this work the structure of the rotational states for low and high vibrational angular momentum is described from the ground state up to the isomerisation barrier using hot gas molecular high resolution spectroscopy and rotationally assigned ab initio rovibronic states. For low vibrational angular momentum the rotational structure of the bending excitations splits in three regions. For J < 40 the structure corresponds to that of a typical linear molecule, for 40 < J < 60 has an approximate double degenerate structure and for J > 60 the splitting of the e and f components begins to decrease and the rotational constant increases. For states with high angular momentum, the rotational structure evolves into a limiting structure for v(2) > 7--the molecule is locked to the molecular axis. For states with v(2) > 11 the rotational structure already begins to accommodate to the lower rotational constants of the isomerisation states. The vibrational energy begins to accommodate to the levels above the barrier only at high vibrational excitations of v(2) > 22 just above the barrier whereas this work shows that the rotational structure is much more sensitive to the double well structure of the potential energy surface. The rotational structure already experiences the influence of the barrier at much lower energies than the vibrational one.

Simple molecules as complex systems

For individual molecules quantum mechanics (QM) offers a simple, natural and elegant way to build large-scale complex networks: quantized energy levels are the nodes, allowed transitions among the levels are the links, and transition intensities supply the weights. QM networks are intrinsic properties of molecules and they are characterized experimentally via spectroscopy; thus, realizations of QM networks are called spectroscopic networks (SN). As demonstrated for the rovibrational states of H216O, the molecule governing the greenhouse effect on earth through hundreds of millions of its spectroscopic transitions (links), both the measured and first-principles computed one-photon absorption SNs containing experimentally accessible transitions appear to have heavy-tailed degree distributions. The proposed novel view of high-resolution spectroscopy and the observed degree distributions have important implications: appearance of a core of highly interconnected hubs among the nodes, a generally disassortative connection preference, considerable robustness and error tolerance, and an “ultra-small-world” property. The network-theoretical view of spectroscopy offers a data reduction facility via a minimum-weight spanning tree approach, which can assist high-resolution spectroscopists to improve the efficiency of the assignment of their measured spectra.

Saddle point localization of molecular wavefunctions

The quantum mechanical description of isomerization is based on bound eigenstates of the molecular potential energy surface. For the near-minimum regions there is a textbook-based relationship between the potential and eigenenergies. Here we show how the saddle point region that connects the two minima is encoded in the eigenstates of the model quartic potential and in the energy levels of the [H, C, N] potential energy surface. We model the spacing of the eigenenergies with the energy dependent classical oscillation frequency decreasing to zero at the saddle point. The eigenstates with the smallest spacing are localized at the saddle point. The analysis of the HCN ↔ HNC isomerization states shows that the eigenstates with small energy spacing relative to the effective (v1, v3, ℓ) bending potentials are highly localized in the bending coordinate at the transition state. These spectroscopically detectable states represent a chemical marker of the transition state in the eigenenergy spectrum. The method developed here provides a basis for modeling characteristic patterns in the eigenenergy spectrum of bound states.

Analysis of (030),(110), and (011) interacting states of D 2 16 O from hot temperature emission spectra

This study is the continuation of our analysis of emission spectra of pure D20. The spectra have been recorded in the 320 - 860 and 1750 - 4300 cm-1 spectral regions at different pressures and temperatures. The measurements were performed in an alumina cell with an effective length of hot gas of about 50 cm. All spectra have been recorded by using the Bruker IFS 120 spectrometer at the Physikalisch-Chemisches-Institut, Justus-Liebig-Universitat Giessen (Germany). More than 5600 lines have been assigned to the second triad {(030), (110), (011)} of interacting states of the D2160 molecule. These transitions were assigned to 24 vibration-rotation and rotational bands. An extended set of more than 1500 experimental rovibrational levels for the (030), (110), and (011) interacting states has been obtained. The maximum values of rotational quantum numbers are Jmax = 30 and Ka max = 21 with Emax = 10568 cm-1 for the (011) state; Jmax = 29 and Ka max = 21 with Emax= 10540 cm-1 for the (030) state, and Jm 26 and Ka max 22 with Eniax 10488 cm1 for the (110) state. A comparison of the observed energy levels with the best available values from literature and with the global prediction is discussed.

Absolute FT-IR Line Positions with a Relative Error of 10-10

With very accurate calibration standards the accuracy of HR-FT spectra can be as high as 10-10. We present the program AUTOCALIB, designed for the automatic calibration of spectra. Using this program we found some problems related to very accurate spectra. Finally we present a CO measurement with a relative error of 4 × 10-10.

A Partial Structure of the Anti Rotamer of 1,2-Difluoroethane from the Analysis of a Band in the High-Resolution Infrared Spectrum

Two regions in the infrared spectrum of gaseous 1,2-difluoroethane at room temperature have been investigated at high resolution. Although bands due to the abundant gauche rotamer dominate the spectrum, a C-type band centered at 3001.89 cm-1 and a largely B-type band centered at 284.260 cm-1 have been shown to be due to the anti rotamer. From its rotational structure the C-type band is confirmed as being due to ν7, the antisymmetric CH2 stretching mode of au symmetry. The B-type band is due to ν18, which is largely the antisymmetric CF bending mode of bu symmetry. The rotational structure of the B-type band, recorded with exceptional resolution in a difficult spectral region, has been analyzed in detail. From the assignment of over 2000 lines, rotational constants have been fitted to the ground state and the upper state. The ground state constants are 1.057 385 7 (11), 0.129 390 34 (26), and 0.120 654 86 (19) cm-1 for this near-prolate symmetric top (κ = −0.9813). These rotational constants imply an incre...