Antisite defects in Sb2-xBixTe3 mixed crystals

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).

Direct Use of the Gradient for Investigating Molecular Energy Surfaces

Why is azulene blue and anthracene white? a simple mo picture

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.

Triplet‐Triplet Spectroscopy of Polyacenes

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...

Jiří Pancíř

Papers

Electronic spectra and semiempirical calculations on dinegative ions of acenaphthylene, fluoranthene and aceheptylene

Physical properties and chemical reactivity of alternant hydrocarbons and related compounds. XVIII. Electronic spectra of arylmethyl cations

Electronic structure of non-alternant hydrocarbons, their analogues and derivatives. III. Ions of the polyenylcyclopentadienyl type

Nature of stationary points on CNDO/2 energy hypersurfaces of van der Waals molecules formed by polar molecules

Adsorption of carbon monoxide on the iridium fcc (112) surface: Topological study