G. Van Hooydonk

Analysis with micro-Raman spectroscopy of natural organic binding media and varnishes used in art

Micro-Raman spectroscopy (MRS) allows the identification of binding media and varnishes in paintings. This non-destructive micro-analytical method has been used for the recording of spectra (1800‐200 cm 1 ) of different types of proteinaceous (albumin, casein, gelatin, isinglass, fish glue), polysaccharide (starch, gum arabic, tragacanth, cherry gum), fatty acid (beeswax, linseed oil, poppy-seed oil, walnut oil, sunflower oil) and resinous media (shellac, dammar, colophony, sandarac, copal, elemi, Venice turpentine, Strasbourg turpentine, amber, mastic, dragon’s blood, gamboge). The Raman spectra can be used as a reference for fingerprinting unknown binders and varnishes. This is demonstrated by the identification of the binder and pigment in a sample of a medieval illuminated manuscript. ©2000 Elsevier Science B.V. All rights reserved.

A bibliotheconomic analysis of the impact factors of scientific disciplines

An attempt is made to correlate bibliometric data of journals (impact factors, half-life) for scientific disciplines in the exact sciences to bibliotheconomic data (subscription prices, prices per article and holdings). Data are presented for 5399 journals in 131 disciplines, as mentioned in theJournal Citation Reports 1900 (Science Citation Index).

A new application of the Kratzer pseudopotential in theoretical chemistry

Abstract The Kratzer pseudopotential is applied to two center chemical systems. The resulting energy expressions are formally consistent with those obtained from standard semi-empirical quantum mechanical procedures. The advantages of the Kratzer expressions however are: (a) the validity of the Pauling—Sherman approximation for the resonance integral can be demonstrated; (b) one-electron energies are redefined unambiguously; (c) the equilibrium values of the coefficients a and b in the wave equation ψ A B = a ψ A + b ψ B are directly obtained as a function of these one-electron energies (diagonal matrix elements); (d) the empirical Pauling bond energy equation is reproduced in the first pproximation; (e) the electronegativity-equalization principle of Sanderson is shown to be completely equivalent with the final result of a variational treatment in semi-empirical quantum-mechanical methods. A stringent spectroscopic confirmation is provided by the theoretical reproduction of a lower order spectroscopic constant for a variety of 38 diatomics. These results are in favour of an anti-PPP method, of which the basis is algebraically related to the usual PPP method. A new expression is derived for the critical distance, determining the ionic-covalent crossing point.

The vibrational spectra of the methylbromogermanes

Abstract The IR and Raman spectra of the methylbromogermanes have been measured. Vibrational assignments are proposed based on characteristic group frequencies, rotational splitting in the IR (in gas phase) and Raman polarisation data.

Standardizing relative impacts: estimating the quality of research from citation counts

The relative impact of local research units is obtained by dividing the observed number of citations to their publications by the expected number of citations. It is argued that the expected citation rates used in the standard method cannot lead to relevant bibliometric scores for specific research topics. Extracting information about quality of research with the standard method is, therefore, almost impossible. The existence of empirical relations between the number of citations and the number of publications for scientific disciplines and for journals, leads to alternative ways to determine relative impact. Hereby, reference data are taken from within a given research topic. Only observed citation and publication (activity) patterns for research topics are taken into account for calculating bibliometric scores. The new methods are not restricted to ISI-publications. The resulting bibliometric scores can contain information about the quality of research, and lead to different rankings than those obtained with the standard method, although the same citation and publication data are used.

On the existence of absolute Pauling electronegativities

Abstract From a reappreciation of the recently proposed Parr—Pearson scheme on absolute electronegativity and hardness, it follows that electron affinities can be considered as absolute Pauling electronegativities. The fundamental difference between Pauling and Mulliken electronegativities is demonstrated. A quantumchemical framework of Huckel-type is developed wherein these electron affinities act as one-electron energies (diagonal matrix elements). This novel definition of absolute Pauling electronegativities is shown to be consistent with Paulings original bond energy equation. The validity of the deductions made implies a possible new look at chemical exchange forces in terms of intra-atomic charge-invariance effects (atom—antiatom interactions).

Further applications of charge-invariance effects upon chemical interactions

Abstract A recently introduced quasi-classical quantum theory of the chemical bond, based upon intra-atomic charge-invariance symmetry effects, is applied to various bonding problems: the organic pi-bond, unsaturated hydrocarbons, ionic bond types and intermolecular bonding. An energetical key to the symmetry based Woodward—Hoffmann rules is presented. Dynamic symmetry effects could also be responsible for chromosome stability and may eventually classify cancer as a quantum disease.

Higher order spectroscopic constants and ionic potentials in molecular spectroscopy

Ionic Kratzer-type potentials (such as the Varshni V-potential) are shown to be consistent with all observed lower- and higher-order spectroscopic constants αe, ωeχe, βe and γe for over thirty diatomics of widely differing ionic characters. All higher Dunham coefficients can be derived from the first, which is itself related to the force constant. The ionic potentials are compared with other potentials discussed in the literature (Dunham, Morse, Simons—Parr−Finlan, Jordan). The deviations of Morse curves near re from RKR-curves are completely predictable using an ionic potential as reference. The Calder-Ruedenberg constant, applicable to 160 diatomics, is consistently accounted for. Calculated vibrational levels for Li2 on both sides of the minimum correspond with experimental levels within 0.6%, whereas computed ΔG(υ)-values are accurate to within 1%. For the excited state, A 1Σu+ of Li2 the same potential is also satisfactory. An ionic potential corrected for an atomic dissociation limit at r = ∞ produces a finite solution at r ≈ 0. In the case of Li2 the energy at r ≈ 10−4 A is of the same order of magnitude as the experimental fusion energy of two Li-nuclei into a single C-nucleus.

Gauge symmetry, chirality and parity effects in four-particle systems: Coulomb's law as a universal function for diatomic molecules.

Abstract Following recent work in search for a universal function (Van Hooydonk, Eur. J. Inorg. Chem., (1999), 1617), we test four symmetric ± a n R n potentials for reproducing molecular potential energy curves (PECs). Classical gauge symmetry for 1/ R -potentials results in generic left–right asymmetric PECs. A pair of symmetric perturbed Coulomb potentials is quantitatively in accordance with observed PECs. For a bond, a four-particle system, charge inversion (a parity effect, atom chirality) is the key to explain this shape generically. A parity adapted Hamiltonian reduces from ten to two terms and to a soluble Bohr-like formula, a Kratzer (1− R e / R ) 2 potential. The result is similar to the combined action of spin and wave function symmetry upon the Hamiltonian in Heitler–London theory. Analytical perturbed Coulomb functions varying with (1− R e / R ) scale attractive and repulsive branches of PECs for 13 bonds H 2 , HF, LiH, KH, AuH, Li 2 , LiF, KLi, NaCs, Rb 2 , RbCs, Cs 2 and I 2 in a single straight line. The 400 turning points for 13 bonds are reproduced with a deviation of 0.007 A at both branches. For 230 points at the repulsive side, the deviation is 0.003 A. The perturbed electrostatic Coulomb law is a universal molecular function. Ab initio zero molecular parameter functions give PECs of acceptable quality, just using atomic ionisation energies. The function can be used as a model potential for inverting levels and gives a first principles comparison of short- and long-range interactions, important for the study of cold atoms. Wave-packet dynamics, femto-chemistry applied to the crossing of covalent and ionic curves, can provide evidence for this theory. We anticipate this scale/shape invariant scheme applies to smaller scales in nuclear and high-energy particle physics. For larger gravitational scales (Newton 1/ R potentials), problems with super-unification are discussed. Reactions between hydrogen and antihydrogen, feasible in the near future, will probably produce normal H 2 .

Measuring impact by a full option method and the notion of bibliometric spectra

A full option method for determining impact takes into account citations to all cited publications, instead of limiting the analysis to ISI-publications only, as usually done in the standard method. The method was tested for the 258 early Ghent professors, teaching in 6 different faculties. The impact of monographs is, in general, much larger than the impact of articles (whether of ISI-type or not). This result remains valid for all six faculties separately. Limiting the bibliometric visibility to ISI-publications reduces the number of citations to only 16%. Bibliometric spectra are presented, in which citations, cited publications and their impact are shown in function of the year of publication. The number of cited publications is always important to expose the influence of activity (production) upon bibliometric scores. For the faculty of Arts, the citations to early professors are compared with those obtained for the presentday generation: the bibliometric spectrum for the former group is rather discontinuous (showing a large erosion in the number of citations by year), whereas that of the latter is continuous. The Ghent citation data are also compared with those given internationally in the same period.