Henryk Chojnacki

Theoretical model for the double fluorescence of p-cyano-N,N-dimethylaniline in polar solvents

Abstract The energies of the low lying electronic states of p -cyano-N,N-dimethylaniline (CDMA) in its planar and in 90° twisted conformation have been calculated using the modified INDO method. Solvent effects have been taken into account. The results agree reasonably well with the experimental data and support the hypothesis of the dual fluorescence of CDMA as being related to the intramolecular rotation of the N(CH 3 ) 2 group, with a decisive role of the solvent polarity.

Ab initio second-order Møller-Plesset calculation of the vibrational spectra of C4 clusters☆

Abstract Second-order Moller-Plesset calculations on the C 4 potential surface yielded three isomers, a linear triplet and rhombic and tetrahedral singlets. A large discrepancy between observed and calculated frequencies of the Σ u + vibration of linear 12 C 4 is outside the expected range of error. It is tentatively suggested that an observed absorption at 1544 cm −1 previously assigned to C 5 might belong instead to C 4 .

QUANTUM CHEMICAL STUDY OF SIMPLE POSITRONIC SYSTEMS USING EXPLICITLY CORRELATED GAUSSIAN FUNCTIONS - PSH AND PSLI+

The electronic structure of positronium hydride has been studied using explicitly correlated Gaussian functions. The resulting energy constitutes new upper bound to the exact nonrelativistic energy of PsH within the Born–Oppenheimer approximation. The two photon annihilation rate was computed using the optimized wave function. Preliminary results for the positron bonded with the lithium atom indicate the stability of this system against the dissociation into Li+ cation and Ps atom.

Configuration interaction study of the positronic hydrogen cyanide molecule

Using the configuration interaction approach, we have revealed that the positronic HCN molecule is energetically stable. The dependency of the positron binding energy on the molecular basis set was studied as well. The use of the basis set constructed explicitly for the sake of polarizability calculations shows that the binding energy of positron to HCN can be as big as about 1.3 mhartree. This article is dedicated to Professor Andrzej J. Sadlej on the occasion of his 65th birthday anniversary.

Structure, Properties and Cytostatic Activity of Triorganotin (Aminoaryl)carboxylates

The properties of vinyltin and phenyltin complexes [Sn(CH=CH2)3{μ-OOCC6H3(NH2)2-3,4}]n (1), [Sn(C6H5)3{OOCC6H3(NH2)2-3,4}] (2), [Sn(C6H5)3{OOC-2-C6H4N=NC6H4N(CH3)2-4}] (3) and [Sn(CH=CH2)3{OOC-2-C6H4N=NC6H4N(CH3)2-4}] (4) have been investigated. The structures of complexes 1, 2, and 3, have been determined by X-ray crystallography. Compound 1 is a distorted trigonal-bipyramidal complex and compounds 2 and 3 adopt a distorted tetrahedral structure. Complex 1 is a single-strand polymer with a bridging 3,4-diaminobenzoato ligand coordinating via the O(1) atom of the carboxylato group and the nitrogen atom of the para-amino group. The oxygen and nitrogen atoms occupy the axial coordination sites. The Sn(1)−N(2A) bond is weak. In complexes 2 and 3 the carboxylato ligands are strongly coordinated to the central atom via one oxygen atom, and the Sn(1)−O(2) distances are considerably longer. Weak interactions of the central atom with the amino group in complex 1, and with the O(2) atoms in complexes 2 and 3, as well as the hydrogen bonds, stabilize the crystal structure. The complexes are effective cytostatic agents. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)

On the reliability of the SCF and CI wavefunctions for systems containing positrons

Abstract The energies and electron—positron collision probabilities for complexes of a positron with one- and two-electron atoms of variable nuclear charge have been studied. In the case of a one-electron atom quantum chemical calculations within the correlated functions approach have also been performed. The results obtained suggest that the energy of the complex can be reproduced relatively well at the CI level, but it requires the use of a flexible basis set. However, it is practically imposible to obtain reliable values of the collision probability. An alternative method of estimation of the electron—positron collision probability has been proposed. It is based on an equation relating the cusp value with the relevant collision probability.

Structure, properties and in vitro cytotoxic activity of hexakis(2-cyanoethyl)ditin(III).

The structure of the tin(III) complex [Sn(2)(CH(2)CH(2)CN)(6)] has been determined. There are two independent molecules in the crystal, both adopt distorted eclipsed conformation. The molecular and electronic structures of this compound have been studied both at the semiempirical level and with the use of non-empirical ab initio methods. The calculated Sn-Sn distances agree well with those found crystallographically. The results of calculations showed that the eclipsed conformation of complex is more stable as compared with staggered conformation. The compound show modest cytotoxic activity against A549 and HSMC cells.

Helical superstructure and charged polarons contributions to optical nonlinearity of 2-methyl-4-nitroaniline crystals studied by resonance Raman, electron paramagnetic resonance, circular dichroism spectroscopies, and quantum chemical calculations.

The Raman excitation profiles of solid 2-methyl-4-nitroaniline (MNA) reveal several band enhancements by intermolecular and intramolecular charge transfer states. Calculated excited- and ground-state molecular geometries and excited state distortions qualitatively determined from Raman spectra indicate multiple vibrations leading to MNA dissociation. Also, overtones and combination tones can generate charged polarons, as detected by electron paramagnetic resonance after the exposure to 980 and 1550 nm laser diodes. The MNA space group Ia (C(s)(4)) is nonchiral; however, the electronic circular dichroism (CD) spectra of solution, KBr pellet, and single crystal were recorded. The crystal chirality is elucidated by room-temperature dynamic disorder, possible helical superstructure along the [102] polar axis, and charged polarons presence. The CD spectra ab initio calculations for MNA neutral and negatively charged monomers, dimers, and trimers, lying along the helix, confirmed the chirality. The role of these findings toward efficient optical nonlinearity and electric conductivity failure is discussed.

A study of photochromic sydnones: structure of the sydnone ring

Abstract The chemical structure of the sydnone ring O(1)-N(2)-N(3)-C(4)-C(5) is discussed using X-ray structural data and results of theoretical calculations obtained by the INDO method. The ring is semiaromatic, the N(2)-N(3)-C(4)-C(5) part being conjugated. The exocyclic C(5)-0(6) bond is close to a double bond and participates in the conjugation.

Adiabatic potentials for the interaction of atomic antihydrogen with He and He

Potential energy curves for interactions of antihydrogen atoms with singlet and triplet states of helium atom and helium cation have been calculated within the adiabatic approximation. The leptonic Schrodinger equation was solved variationally with the basis of explicitly correlated Gaussian functions. Adiabatic corrections have been calculated with the Born–Handy method. For the and systems, critical distances have been found to be below 1.7 bohr and 1.0 bohr and the rearrangement cross sections have been computed with the semiclassical method. The possible existence and structure of complex atomcules is discussed.