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Jiří Pancíř

Bio: Jiří Pancíř is an academic researcher from Czechoslovak Academy of Sciences. The author has contributed to research in topics: Chemisorption & Hypersurface. The author has an hindex of 9, co-authored 25 publications receiving 247 citations.

Papers
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Journal ArticleDOI
TL;DR: In this article, a double iteration technique was used to determine the equilibrium geometry within the framework of a single calculation of the energy function for the ground state and the lowest excited singlet state of formaldehyde and for the formyl radical.
Abstract: The author suggests a procedure offering the possibility to determine, with the use of a double iteration technique, the equilibrium geometry within the framework of a single calculation of the energy function. The method is used for the ground state and the lowest excited singlet state of formaldehyde and for the formyl radical. The individual contributions of the potential energy are discussed in brief.

38 citations

Book
01 Aug 1970

27 citations

Journal ArticleDOI
TL;DR: In this article, a force constant matrix analysis of the INDO energy hypersurface for various orientations of ethylene in external electric fields of the strength F = 0, 2, 4, 6, 8 and 10 × 1010 V m−1 was performed.
Abstract: Stationary points of the INDO energy hypersurface for various orientations of ethylene in external electric fields of the strength F=0, 2, 4, 6, 8 and 10 × 1010 V m−1 were found and their characteristics studied by the force constant matrix analysis. Energies, structural parameters, charges, Wiberg indices and dipole moments are presented. The only stable orientation of the ethylene molecule is that for which the CC bond is parallel to the field direction up to F=6 × 1010 V m−1 (orientation (a) in Fig. 1). Above this value the molecule is structurally unstable and it decomposes to the hydride anion and the C2H3+ cation. Rotational instability was found for two perpendicular orientations of the CC bond with respect to the field vector, in which the field vector was parallel and perpendicular to the molecular plane. Pseudorotations with negative eigenvalues of force constant matrices lead to the stable orientation (a). No stationary points were found when the angle between the CC bond and the field vector was between 0 and 90°. The five longest wavelength vibrational bands are presented for selected orientations and field strengths.

24 citations


Cited by
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Journal ArticleDOI
TL;DR: In this article, the energy of formation of antisite defects in Sb 2− x In x Te 3 crystals has been determined for x = 0.0-0.4, these values lying in the range 0.35 -0.44 eV.

166 citations

Book ChapterDOI
01 Jan 1977
TL;DR: In this paper, the authors proposed a power series expansion method to characterize a multidimensional potential surface, i.e., by its derivatives with respect to the nuclear coordinates, and evaluated these derivatives from a pointwise calculation of the energy, followed by a fitting procedure.
Abstract: A great deal of chemical and spectroscopical processes involve the relative motion of atomic nuclei. For most low-energy processes the Born-Oppenheimer fixed-nuclei approximation is sufficient: the nuclear motion takes place on an effective potential surface which is the sum of the electronic energy and the nuclear repulsion as a function of the nuclear coordinates. One of the main fields of quantum chemical activity is the study of these surfaces. Complete characterization of a multidimensional potential surface is a very complex task. Often, however, the nuclear motion takes place in the vicinity of a reference configuration, and the surface can be adequately characterized by a power series expansion, i.e., by its derivatives with respect to the nuclear coordinates. Traditionally, these derivatives have been evaluated from a pointwise calculation of the energy, followed by a fitting procedure. This method has some serious drawbacks both in efficiency and in numerical accuracy. Indeed, Hartree(1) observes that “the differentiation of a function specified only by a table of values ... is a notoriously unsatisfactory process, particularly if higher derivatives than the first are required” (see Gerratt and Mills(2) for examples).

163 citations

Journal ArticleDOI
TL;DR: In this paper, it was shown that despite their almost identical ionization potentials and electron affinities, azulene and anthracene differ considrably in their lowest singlet-singlet excitation energies.

137 citations

Journal ArticleDOI
TL;DR: In this article, the LCAO-MO-SCF Pariser-Parr-Pople method was used to estimate the ππ* triplet states energies with the use of large configuration interactions.
Abstract: Complete triplet—triplet absorption spectra (2000–10000 A) were measured in alcoholic solution at 113°K with naphthalene, anthracene, tetracene, and a few methylated derivatives. Several new bands were observed. Calculations of the higher ππ* triplet states energies with the LCAO—MO—SCF Pariser—Parr—Pople method were improved by the use of large configuration interactions. These include many doubly excited configurations with respect to both the ground singlet state S0 and the lowest triplet state T1, thanks to the systematic use of all monoexcitations with respect to S0 plus all monoexcitations with respect to T1. The comparison of all experimental and theoretical results for the three polyacenes allows one to modify a few previous assignments and to give a general tentative assignment for all observed transitions.

135 citations

Journal ArticleDOI
TL;DR: In this paper, the structure of chemisorbed CO on the steps of Pt(112) {Pt[3(111)×(001)]} was monitored as a function of coverage by the digital electron stimulated desorption ion angular distribution method (ESDIAD), digital low-energy electron diffraction (LEED), and temperature-programmed Desorption (TPD).
Abstract: The structure of chemisorbed CO on the steps of Pt(112) {Pt[3(111)×(001)]} was monitored as a function of coverage by the digital electron stimulated desorption‐ion angular distribution method (ESDIAD), digital low‐energy electron diffraction (LEED), and temperature‐programmed desorption (TPD). The ESDIAD method applied to the desorption of an electronically excited, neutral CO species (the metastable a3 π‐CO state) avoids the influence of image potential effects on the trajectory of desorbing species, yielding true desorption angles, equivalent to Pt‐CO bond orientations. CO adsorbs exclusively on step sites at low coverage with a 20° ‘‘downstairs’’ tilt from the [112] direction (designated ‘‘0°’’). LEED indicates (2×n) order (i.e., two‐fold order along the steps but no order up/down the steps) exists when the steps are half‐filled (about 0.19 ML). At 0.24 ML, CO is still adsorbed only on the step sites but one‐dimensional CO–CO repulsions between nearest neighbors result in CO tilting along the steps. T...

108 citations