bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Intramolecular Hydrogen-Bond in Malonaldehyde as Seen by Infrared Spectroscopy. A Four-Dimensional Model Study
Authors: Došlić Nadja , Kühn O. 
Published: December 2003

Abstract
The infrared spectrum of the O–H–O fragment of malonaldehyde is studied using a four-dimensional model. This comprises the OH stretching and the two OH bending vibrations as well an O–O ring deformation mode under the assumption of overall Cs symmetry. The full anharmonic potential energy and dipole moment surfaces are calculated using density functional theory and the respective vibrational eigenvalue problem is solved by an iterative Lanczos method. Fundamental and combination transitions are discussed for the normal species and the symmetrically deuterated isotopomer. Special emphasis is paid to the OH/OD stretching region which reveals the signatures of strong mode mixing what renders a simple assignment in terms of fundamental transitions difficult. In addition results for hot transitions are presented which show a rather different OH/OD band due to the topology of the potential energy surface. The influence of H atom tunneling on the spectrum is briefly addressed employing an alternative three-dimensional model which takes into account the in-plane H atom motion as well as the O–O distance.
Proton Transfer to Organometallic Hydrides via Unconventional Hydrogen Bonding: Problems and Perspectives
Authors: Belkova N. V. , Gutsul E. I. , Shubina E. S. , Epstein L. M. 
Published: December 2003

Abstract
This review summarizes the spectral and theoretical results concerning different ways of proton transfer through hydrogen bonds (HB) to metal atoms (XH···M) and hydride ligands (XH···HM) leading to classical and nonclassical cationic hydrides. The spectral (NMR, IR, UV-Vis in the temperature range 190–290K) and theoretical studies of the structural and energetic characteristics of HB intermediates and proton transfer allow the representation of the experimental energy profiles. The problems concerning the influence of different factors on the processes and potential energy surfaces requiring active investigations in this new area are discussed
Synthesis of Monodisperse Heptanol Stabilized Ruthenium Nanoparticles. Evidence for the Presence of Surface Hydrogens
Authors: Pelzer Katrin , Philippot Karine , Chaudret Bruno 
Published: December 2003

Abstract
The decomposition of Ru(cod)(cot) (1; cod = 1,5-cyclooctadiene, cot = 1,3,5-cyclooctatriene) under an H2 atmosphere (3 bars) in pure heptanol produces crystalline monodisperse nanoparticles of 3nm mean size characterized by TEM and WAXS techniques. Solution NMR studies demonstrate the presence of surface hydrogens due to the synthesis process and suggest a fast exchange between free and coordinated heptanol molecules.
Interpretation of Hydrogen/Deuterium Isotope Effects on NMR Chemical Shifts of [FHF]− Ion Based on Calculations of Nuclear Magnetic Shielding Tensor Surface
Authors: Golubev Nicolai S. , Melikova Sona M. , Shchepkin Dimitri , Shenderovich Ilja G. , Tolstoy Peter M. , Denisov Gleb S. 
Published: December 2003

Abstract
Using ab initio calculations of 1H, 19F magnetic shielding tensors of hydrogen difluoride ion as the functions of three coordinates of symmetry, an attempt is made to estimate the contributions of different vibrational isotope effects to H/D NMR isotope shifts referred in the literature. It is shown that the contributions of the amplitudes of proton stretching and bending vibrations dominate whereas the contribution of the totally symmetric vibration can be neglected. Different signs of the H/D isotope effects on hydron and fluorine chemical shifts are caused by very strong angle dependence of the fluorine magnetic shielding. The agreement of the calculated and measured values is nearly quantitative. An unusually strong paramagnetic deshielding of hydrogen for the equilibrium geometry of the [FHF]− ion is noted.
Computed EOM-CCSD 19F-19F Spin-Spin Coupling Constants in Small Organic Molecules
Authors: Del Bene Janet E. , Alkorta Ibon , Elguero José 
Published: December 2003

Abstract
Two-, three-, and four-bond 19F-19F spin-spin coupling constants (
nJ
FF) for a set of small fluoro-substituted organic molecules have been computed using ab initio equation-of-motion coupled cluster singles and doubles (EOM-CCSD) theory. The computed values reproduce the experimental signs and magnitudes of
nJ
FF. The straight line that relates the experimental and computed coupling constants has a slope of approximately 1 and passes through the point (0,0 Hz) within the uncertainties of the fit. Hence, EOM-CCSD values of
nJ
FF should be excellent predictors of experimental values when these are not available. All of the components of
nJ
FF except for the diamagnetic spin-orbit term may be large and must be evaluated if agreement between theory and experiment is to be obtained.
Quantum Simulations for Isotope Effects of IR + UV Laser Pulses on Symmetry and Selective Hydrogen Bond Breaking
Authors: Elghobashi Nadia , González Leticia , Manz Jörn 
Published: December 2003

Abstract
Intense few-cycle femtosecond (fs) infrared (IR) laser pulses yield dynamical symmetry breaking of oriented strong symmetric hydrogen bonds A···H···A due to nearly coherent vibrational excitation. Consequently, the system evolves with alternate stretches or compressions of the competing bonds A···H and H···A. For a specific stretch of, say, the H···A bond, an ultrashort ultraviolet (UV) laser pulse may induce a nearly instantaneous electronic excitation and/or photo-detachment by means of a Franck–Condon(FC)-type transition to a dissociative potential energy surface of the excited state. The stretched bond, H····A, will then dissociate selectively, yielding preferably the products AH+A. A minor fraction of the other products A+HA may also be formed due to competing wavepacket dispersion. The corresponding isotope effects are investigated by means of the representative laser driven molecular wavepackets which are propagated on ab initio potential energy surfaces and with ab initio dipole coupling for the model systems, FHF− versus FDF−. The resulting quantum dynamics for both systems are nearly equivalent if the driving IR laser fields are scaled with decreasing carrier frequency and amplitudes and increasing durations for the corresponding increasing masses of the isotopomers.
Influence of Cation Exchange on the27Al-NMR Spectra of Zeolites
Authors: Masierak W. , Emmler T. , Buntkowsky Gerd , Gutsze A. 
Published: December 2003

AbstractThe influence of cation exchange on the27Al-NMR spectra of NaA-zeolites has been studied by27Al-MAS- and MQ-MAS-Solid State-NMR. From the27Al-spectra a characterization of the different Al sites in the A zeolites according to their chemical environment and the structural changes on the aluminosilicate network caused by the cation exchange are obtained. It is found that the exchange with cations with smaller ion-radius cause stronger distortions of the27Al-NMR-spectra than exchange with larger cations like Ba2+. Employing MQ-MAS spectroscopy these distortions are revealed as second order quadrupolar effects for the smaller cations and as a combination of chemical shift and second order quadrupolar interaction for the Ba cation. These changes of the quadrupolar coupling are interpreted numerically via calculations of the lowering of the symmetry of the EFG tensor. Finally it is found that the exchange with divalent cations leads to distortions of the zeolitic framework and the formation of an extra-framework aluminum. To the best of our knowledge this is for the first time that evidence for the production of extra frame work aluminum by pure cation exchange without any thermal treatment has been found in type A zeolites.
Solid State NMR Connectivity Studies in Dipolarly Coupled Inorganic Networks: Site Assignments in the Solid Electrolyte Material (CuI)8P12
Authors: Brunklaus Gunther , Chan Jerry C. C. , Eckert Hellmut 
Published: December 2003

Abstract
The local structure of the fast solid ion conductor Cu2P3I2 = (CuI)8P12 is investigated using one- and two-dimensional 31P and 65Cu magic-angle spinning NMR techniques. Peak assignments are proposed on the basis of anisotropic and isotropic spin-spin interactions recovered via radio frequency driven dipolar recoupling (RFDR) and total through bond correlation spectroscopy (TOBSY) methods. Especially the previously proposed R306
14 pulse symmetry (R-TOBSY), which exploits scalar spin-spin interactions for coherence transfer, offers outstanding spectral selectivity with respect to 1
J coupling. Using sufficiently short mixing times it is thus possible to correlate selectively those 31P spins that are directly bonded, thereby providing detailed insights into phosphorus-phosphorus connectivities in the network. The final assignment of the nine resolved 31P resonances to the twelve crystallographically distinct phosphorus sites suggests a significant relationship between 31P chemical shifts and the detailed pyramidal P(P1/3)3 bonding geometry.
2D NMR Nutation Analysis of Non-Thermal Polarization of Coupled Multi-Spin Systems
Authors: Ivanov K. L. , Miesel K. , Vieth Hans-Martin , Yurkovskaya A. V. , Sagdeev R. Z. 
Published: December 2003

Abstract
A new, convenient method of analyzing the spin polarization of a non-equilibrium system of N coupled nuclei is described and applied to photo-reactions exhibiting chemically induced dynamic nuclear polarization (CIDNP). It is based on the Fourier analysis of the variation of NMR line intensities as a function of the radio frequency excitation pulse length. A relationship between the spectral components at various harmonic order and the alignment in the spin multiplet is established. In application to the Norrish type I photolysis of cyclodecanone we demonstrate that at low magnetic field the rate determining step in the reaction kinetics depends on the mutual orientation of at least four pairs of non-equivalent spins.
The Characterization of Metal–Metal Bonds in Unsaturated Binuclear Homoleptic Transition Metal Carbonyls. The Compliance Matrix
Authors: Xie Y. , Schaefer H. F. 
Published: December 2003

Abstract
The compliance matrix (inverse force constant matrix) has been used to estimate metal–metal bond character for the homoleptic transition metal carbonyls Fe2(CO)
n
and Co2(CO)
n
. The results are often in agreement with other methods, but the compliance matrix provides a unique measure while other methods may be ambiguous. The more unsaturated compounds with fewer carbonyls have stronger metal–metal linkages, indicating a general, if not infallible, correlation between the diagonal compliance matrix element and the formal bond order, given by the 18-electron rule. It is found that the apparent metal–metal bond strength, as judged by the compliance matrix, is significantly enhanced by the bridging (as opposed to terminal) carbonyls. Thus one must only make precise comparisons between systems with the same numbers of bridging carbonyls.
Quantum Chemical Investigation of Spin-Forbidden Transitions in Dithiosuccinimide
Authors: Tatchen J. , Kleinschmidt M. , Marian C. M. , Parac M. , Grimme S. 
Published: December 2003

Abstract
The vertical and adiabatic electronic spectra of dithiosuccinimide have been investigated by means of multi-reference Møller–Plesset perturbation theory and combined densitiy functional/multi-reference configuration interaction methods. Geometries of the electronic ground state and several low-lying excited states have been optimised at the level of time-dependent density functional theory. We have determined spin-orbit coupling for correlated wavefunctions utilising a non-empirical spin-orbit mean-field approach. Because of the two thiocarbonyl groups present in the molecule, dithiosuccinimide exhibits a dense spectrum of low-lying valence states. The first two excited singlet states (S
1 and S
2) originate from n → π* excitations. Nearby, three triplet states are located, two n → π* states (T
1 and T
2), and a π → π* triplet excitation (T
3). The experimentally observed strong absorption band with maximum at 3.96 eV arises from the π → π* excited 1
B
2 (S
3) state. Computed radiative lifetimes are presented for the experimentally known phosphorescence from the n → π* excited T
1 state. Further, we find nearly equal probabilities for the spin-forbidden S
0 → T
2 and the spin-allowed S
0 → S
1 transitions in absorption. On these grounds, we assign band number 3 in the spectra measured by Meskers et al. [J. Phys. Chem.
99 (1995) 1134] to this spin-forbidden transition.
Rovibronic States in the X
2
Π State of the CCS− Anion
Authors: Panten D. , Chambaud G. , Rosmus P. , Riaplov E. , Maier J. P. 
Published: December 2003

Abstract
Three-dimensional potential energy functions have been generated ab initio for the X
2Π electronic ground state of CCS− and used in variational Renner–Teller calculations including electron spin. Rovibronic levels (J=P) for J≤5/2 are given for energies up to 4000cm−1. The pattern of the levels is compared with that of CCO−. In the case of CCS− the quartic force fields, equilibrium geometry, electric dipole moment, the electronic affinity and the Franck–Condon factors for the X
2Π(CCS−) → X
3Σ− (CCS) photodetachment spectrum are calculated.
Ab initio MRD-CI Study of the Electronic Spectrum of Tribromomethanol Br3COH and the Photofragmentation along Br–C and C–O Cleavage
Authors: Mühlhäuser M. 
Published: December 2003

Abstract
Multi reference configuration interaction calculations are carried out to compute the electronic spectrum of tribromomethanol Br3COH. The first dipole-allowed transitions are computed at 5.0 eV (11
A″ ← X
1
A′) and 5.4 eV (21
A″ ← X
1
A′) followed by three transitions at 5.5 eV (21
A′ ← X
1
A′) and 6.1 eV (31
A′ ← X
1
A′, 31
A″ ← X
1
A′). The largest oscillator strength (f = 0.08) is obtained for the σ → σ* type excitation 31
A″ ← X
1
A′ computed around 6.1 eV. The corresponding triplet states are also given. Five low-lying excited states in the energy range between 4.5 eV and 5.5 eV are found to be highly repulsive for Br–C elongation, leading to Br2CHOH (X
2
A′) and Br (X
2
P), so that tribromomethanol Br3COH is expected to be important for atmospheric chemistry as reservoir of Br radicals. Photodissociation along C–O cleavage resulting in Br3C (X
2
A′) and OH (X
2
Π) has to overcome a barrier of about 0.7 eV because the low-lying excited states 11
A″, 13
A′ and 13
A″ become repulsive only after elongating the C–O bond by about 0.45 Å.
Theoretical Study of the Dissociation and Isomerization of NCS
Authors: Diehr M. , Chambaud G. , Werner H.-J. 
Published: December 2003

Abstract
Large scale MRCI calculations have been performed to study the electronic ground state and low-lying excited states of the NCS molecule and its isomers. The isomer CNS is found to be stable and linear. It lies 1.29 eV higher in energy than NCS, while CSN has a much higher energy and is unstable. The dissociation energy of the NCS isomer has been calculated to be 4.25 eV. The isomerization paths between the 2Π ground states of both isomers have been mapped by CASSCF and MRCI calculations. The barriers for the NCS → CNS isomerization in 2
A′ and 2
A″ symmetry have cyclic forms and the barrier heights have been calculated to be 2.71 eV and 2.44 eV, respectively (MRCI). For both isomers, the collinear dissociation paths to the (diatomic + atom) fragments have been investigated by CASSCF calculations. Spectroscopic data are given for the X
2Π ground state and for the A
2Σ+ state of CNS. The results are compared with the valence isoelectronic system NCO.
Theoretical Study of the Vertical Electronic Spectra, Electron-Spin g-Factors and Hyperfine Coupling Constants of the (C
2v) Cyclic Radicals C3
+, Si3
+, C3
− and Si3
−
Authors: Bruna P. J. , Grein F. 
Published: December 2003

Abstract
The vertical transition energies and Δg-values of cyclic C3
+, Si3
+ (X
2
B
2), C3
− (12
A
1, metastable) and Si3
− (X
2
A
1) are studied with ROHF MOs, multireference (MRDCI) wavefunctions and 6-311+G(2d) basis sets. Si3
− has at least eight bound states. For each radical, the in-plane components of the g shift, Δgyy
and Δgzz
(with gii
= g
e + Δgii
), have similar negative values (about −1200 ppm for C3
+, C3
− and about −8000 ppm for Si3
+, Si3
−). The Δgxx
’s are larger in magnitude, negative for C3
+, Si3
+ (−11000 and −72000 ppm) but positive for C3
−, Si3
− (8000 and 165000 ppm). The hyperfine coupling constants A
iso, A
dip are evaluated with ab initio CISD, QCISD, CCD, MP4SDQ methods as well as with density functional theory (DFT) methods (SVWN, B3LYP, B3PW91, PW91PW91), using a spin-unrestricted formalism; several basis sets are considered. Both approaches give internally consistent A
iso’s and A
dip’s for each X3
− center, with the (positive) s-spin-density at each basal atom (average A
iso (MHz) = 75 for C3
− and −25 for Si3
−) being smaller than at the apical center (275 and −95 MHz). The results are less satisfactory for X3
+. All treatments agree, more or less, in a larger (positive) s-density at the basal atoms (A
iso(MHz) from 300 to 700 for C3
+, and −80 to −150 for Si3
+), whereas the s-contribution at the apical center depends on the method: for C3
+, it is positive with ab initio but negative with DFT, whereas for Si3
+ the opposite trend is found; as well, A
dip(X3
+) shows unusually large discrepancies for each center. For these radicals, literature values of A
iso and A
dip are not available, either from experimental or multireference ab initio studies, to allow for comparisons with our results.
Electrochemical Micromachining of Stainless Steel by Ultrashort Voltage Pulses
Authors: Cagnon Laurent , Kirchner Viola , Kock Matthias , Schuster Rolf , Ertl Gerhard , Gmelin W. Thomas , Kück Heinz 
Published: December 2003

Abstract
Application of ultrashort voltage pulses to a tiny tool electrode under suitable electrochemical conditions enables precise three-dimensional machining of stainless steel. In order to reach submicrometer precision and high processing speed, the formation of a passive layer on the workpiece surface during the machining process has to be prevented by proper choice of the electrolyte. Mixtures of concentrated hydrofluoric and hydrochloric acid are well suited in this respect and allow the automated machining of complicated three-dimensional microelements. The dependence of the machining precision on pulse duration and pulse amplitude was investigated in detail.
Molecular Structure Effects in the Adsorption Behaviour of some Aromatic Heterocyclic Compounds at High-Area Carbon-Cloth in Relation to Waste-Water Purification
Authors: Conway Brian E. , Ayranci Guler , Ayranci Erol 
Published: December 2003

Abstract
Adsorption behaviours of some structurally related aromatic heterocyclic compounds at an high-area carbon-cloth material have been investigated in relation to waste-water purification. Adsorption processes were followed by monitoring the concentration of adsorbates in a specially designed cell using an in situ UV spectrophotometric method. The rates of adsorption were compared by treating the data according to first-order kinetics. Among the seven heterocyclic compounds studied, thiophene was found to exhibit the highest adsorption rate. This was attributed to the presence of the electron-donative S heteroatom in the structure of this compound. The influences of the dipole moment, the orientation at the C-cloth surface and the size of the heterocyclic adsorbate compound, as well as the type of heteroatom in the ring and the adsorbates’ hydration parameters, on the extent of adsorption of these compounds at the C-cloth were investigated.
Frequency Response Analysis of the Potential Modulated Microwave Reflectivity Response of p-Type Silicon During Anodic Dissolution in Ammonium Fluoride Solutions
Authors: Duffy N. W. , Kirah K. , Peter L. M. , Ushiroda S. 
Published: December 2003

Abstract
Interpretation of the impedance of the silicon electrolyte interface is particularly complicated under conditions in which anodic silicon dissolution occurs. In the present work the frequency-resolved potential modulated microwave reflectivity (PMMR) technique has been combined with electrochemical impedance spectroscopy (EIS) to study the behaviour of low-doped p-type silicon in buffered ammonium fluoride. The EIS response is determined by the total impedance of the system, whereas the PMMR response originates from modulation of the hole density in the silicon space charge region. This difference has led to the development of a novel approach to deconvolution of the interfacial impedance. It involves multiplication of the PMMR and EIS responses to give the space charge impedance. Particular attention is focussed on accumulation conditions in the electropolishing region, where the surface of the silicon is covered by a duplex oxide film. The impedance of the accumulation layer is obtained using the new approach, and the oxide impedance is then derived. Analysis of the PMMR results provides convincing evidence that the hole mobility in the accumulation layer is more than an order of magnitude smaller than in the bulk.
Voltammetry and Impedance of Pt(111) Electrodes in Aqueous KClO4 Solutions
Authors: Pajkossy Tamás 
Published: December 2003

Abstract
The voltammetric behaviour of Pt(111) electrodes in neutral and near-neutral aqueous KClO4 solutions (4 < pH < 9.7) is discussed. In this system, within the ideally polarizable potential region, the only processes affecting voltammetry and impedance are the adsorption and desorption of the H+ and OH− ions. Due to the low bulk concentrations of these ions, the desad processes are diffusion controlled. This situation is analysed using cyclic voltammetry, transient and impedance measurements.
Quantitative Modeling of the Oscillatory Electrooxidation of Hydrogen on Pt in the Presence of Poisons
Authors: Plenge F. , Varela H. , Lübke M. , Krischer K. 
Published: December 2003

AbstractA quantitative model of oscillations observed during hydrogen oxidation on platinum in the presence of electrosorbing metal ions and specifically adsorbing anions is presented and the model predictions are compared with experiments. Mass and charge balances of all reactants lead in a first step to a seven variable model which is governed by reaction steps that have been widely studied. We demonstrate that attractive interactions between metal and halide ions on the electrode surface, which were recently reported, are crucial for the observed dynamics. The model parameters were almost exclusively taken out of the literature. The model is then reduced to its minimal form without losing dynamic features arriving at a four variable system. Experimental time series of three of the four variables of the model and measured bifurcation diagrams are presented. It is shown that the integrated time evolution and the calculated bifurcation diagrams of the model agree almost quantitatively with the experiment.
The Concept of Dwell Times in a Kinetic Model of Alloy Deposition
Authors: Plieth W. 
Published: December 2003

Abstract
A model of alloy deposition was developed based on a concept of dwell times of atoms in kink site positions. It was shown that the dwell times, together with the deposition rates of the alloy components are the steering parameters deciding, which atom will be deposited in the different kink sites of the growing alloy. The model provides a basis for quantitative modelling of alloy composition and alloy structure.