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1

Spectroscopy and Photophysics of Monoazaphenanthrenes II. Ab initio Analysis of Molecular Parameters and Electronic Spectra

100%

Deperasińska I., Prochorow J.

Acta Physica Polonica A

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2003

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vol. 104

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issue 6

601-613

EN

The ground state structures of phenanthrene and its monoaza-deriv atives, phenanthridine and 7,8-benzoquinoline were optimized using the ab initio methods. Both methods of optimization are leading to the results, which are in good agreement with available experimental data. Calculated ground-state electric dipole moments in phenanthridine and 7,8-benzoquinoline were found to have antiparallel orientations, due to the different electronic charge distributions in these molecules. The energies of vertical electronic transitions from the ground to excited singlet states (S_0 → S_n transitions) and the corresponding oscillator strengths were calculated within the framework of configuration interaction-singles and time-dependent density functional theory. The last method was found to be more accurate in reproduction of experimental absorption spectra. Very interesting result of these computations is the change of relative orientation of the transition dipole moments for the two lowest ππ* electronic transition in monoazaphenanthrenes - from perpendicular in phenanthrene molecule to nearly parallel orientation in both monoazaphenanthrenes. The observed changes of molecular parameters and spectra can be related to the inductive effects of the substitution of nitrogen atom into the aromatic skeleton of phenanthrene.

2

Natural Bond Orbital (NBO) Population Analysis of 1-Azanapthalene-8-ol

80%

Gangadharan R., Sampath Krishnan S.

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vol. 125

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issue 1

18-22

EN

The molecular structure of 1-azanapthalene-8-ol was calculated by the B3LYP density functional model with 6-31G(d,p) basis set by Gaussian program. The results from natural bond orbital analysis have been analyzed in terms of the hybridization of atoms and the electronic structure of the title molecule. The stability of the molecule arising from hyper conjugative interactions, charge delocalization has been analyzed using natural bond orbital analysis. The electron density based local reactivity descriptors such as the Fukui functions were calculated. The dipole moment (μ) and polarizability (α), anisotropy polarizability (Δ α) and first order hyperpolarizability (β_{tot}) of the molecule have been reported.

3

Fluorescence Spectra of 7,8-Benzoquinoline Isolated in the Supersonic Jet Expansion - An Ab Initio Analysis

80%

Deperasińska I., Prochorow J., Stepanenko Y.

Acta Physica Polonica A

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2004

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vol. 106

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issue 4

535-545

EN

The optimized equilibrium geometry of 7,8-benzoquinoline molecule in its first excited, S_1, singlet state was computed with the use of ab initio RCIS/6-31G(d) method. It was found that the electronic transition to the first excited state in 7,8-benzoquinoline is not confined to the neighborhood of nitrogen atom, but is delocalized over entire aromatic rings system, much alike in the molecule of phenanthrene. With the optimized geometry of the ground and excited state of the molecule, the frequencies of the vibrational fundamental modes were computed, together with their displacement parameters (geometry changes of vibrations between the excited and the ground state). These frequencies are in good agreement with vibrational frequencies present in the fluorescence spectrum of 7,8-benzoquinoline observed recently under jet-cooling conditions in supersonic beam expansion. In comparison to the fluorescence spectrum of phenanthrene, the calculated, as well as experimental fluorescence spectra of 7,8-benzoquinoline contain much more vibrational features, and this increased vibronic activity is related to the symmetry break caused by the introduction of N-heteroatom into the aromatic ring system of phenanthrene.

4

Spectroscopy of 2-aminopurine: An MCSCF Study

80%

Rachofsky E., Ross J., Krauss M., Osman R.

Acta Physica Polonica A

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1998

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vol. 94

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issue 5-6

735-748

EN

2-aminopurine is a highly fluorescent isomer of adenine that can be incorporated into DNA as a probe of structure, dynamics, and protein-DNA interactions. Interpretation of the fluorescence of 2-aminopurine in DNA requires a model of the electronic structure of this fluorophore in its ground and excited states. To this end, electronic structures and energies of the ground and lowest singlet excited states of 2-amino-9-methylpurine were calculated by the multiconfiguration self-consistent field method supplemented by multiconfiguration perturbation theory. The molecular geometry was optimized in both of these electronic states to permit investigation of both electronic excitation and fluorescence emission. The predicted energies and transition dipoles were in good agreement with experiment. The permanent molecular dipole of 2-amino-9-methylpurine increased upon excitation, suggesting that both the absorption and emission spectra should shift to slightly lower energies in polar solvents. The anomalous spectral shifts observed in water suggest that 2-aminopurine undergoes hydrogen bonding that better stabilizes the ground state than the excited state. From the calculated electrostatic potentials of these two states, the position at which this hydrogen bond forms was predicted. These results form a basis for understanding the excited states and possible intermolecular interactions of 2-aminopurine in DNA.

5

Resonant Spin Splitting in III-V Semiconductors

80%

Skierkowski A., Majewski J.

Acta Physica Polonica A

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2005

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vol. 108

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issue 5

867-872

EN

We present first-principles studies of the zero field spin splitting of energy bands in typical III-V semiconductors. Our calculations reveal that the strain induces linear-k spin splitting of the conduction band in theΓ point, which is linear in strain, and determine the magnitude of the so-called acoustic phonon constant that characterizes the magnitude of the spin splitting. In addition, we show that optical phonons lead to spin-flip processes and we present quantitative results for the spin-phonon deformation potentials in GaAs. Most importantly, the calculations show that the linear-k spin splitting can be resonantly enhanced when bands cross in a particular point of the Brillouin zone. This resonant enhancement of the bulk inversion asymmetry coupling constant by more than one order of magnitude was observed in both valence and conduction bands and can be steered by the application of the external stress. This allows tailoring of the spin relaxation and spin precession of conduction electrons in nanostructures to a much larger extent than was hitherto assumed.

6

The Semiempirical Method for Finding Thermal Characteristics of Simple Crystals

80%

Scharoch M.

Acta Physica Polonica A

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2004

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vol. 106

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issue 4

487-495

EN

A method for ab initio (using density functional theory) study of thermal properties of crystalline solids, based on the quasiharmonic approximation, is briefly summarized. On that basis the semiempirical method is proposed which combines the ab initio calculation of the static total energy with the Einstein model of crystal vibration. The Murnaghan equation of states is used as an analytical model for the static total energy. An exponential form of the phonon energy versus volume dependence is introduced which was proved to perform very well. Two parameters appearing in the model are found by fitting to easily available experimental data (tabular or measured). The method then provides thermodynamic characteristics in a large range of temperatures and pressures. On the other hand, the corrections due to the zero-point vibration are provided to some first principles results, like lattice parameters or bulk modulus. An interesting outcome of the model is the pressure dependence of the overheating temperature, for relatively low pressures. Tests performed on the example of fcc aluminum show remarkably good agreement of the results with experimental data. Therefore the method offers a handy tool for fast analysis of thermodynamics of simple crystalline systems, omitting the first principles evaluation of the phonon energies.

7

Molecular Modelling of Interface Occurrence of Ti (C,N,O) - Fe Composite

80%

Biedunkiewicz A., Noworol P.

Acta Physica Polonica A

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2002

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vol. 102

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issue 2

161-165

EN

High demands that are posed to modern materials exposed to the action of thermal, mechanical or chemical loads oblige one to seek new solutions and technologies. Compliance with these expectations requires designing the composite materials without structural notches, and the application of gradient materials. Transient zone, determining the interphase compound, is an essential element of each composite. Interaction forces creating transient structural zones determine the value of the adhesion forces. Among all forces determining the adhesion the strongest are the forces of a chemical bond. Therefore, the molecular modeling should be a valuable method to investigate and design the composites. In the presented research the conditions of coat adhesion of the Ti (C,N,O)-type to steel substrate are taken into consideration. Using a standard quantum-chemistry program, the energies of the following systems (clusters) - Fe-α- N-Ti, Fe-α-C-Ti, and Fe-α-O-Ti - are calculated. The aim of the analysis was to determine the conditions for preparation of initial substrate, which are advantageous for the process of coat formation. This analysis confirmed benefits arising from nitriding as an initial treatment of the steel.

8

Fluorescence Spectra of Phenanthridine Isolated in the Supersonic Jet Expansion - An Ab Initio Analysis

80%

Deperasińska I., Prochorow J., Stepanenko Y.

Acta Physica Polonica A

|

2005

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vol. 108

|

issue 6

1005-1019

EN

Following the analysis of laser induced fluorescence spectrum of 7,8-benzoquinoline molecule, observed under conditions of isolation in the supersonic jet expansion, the ab initio analysis of laser induced fluorescence spectrum of phenanthridine, observed under the same experimental conditions, was performed. This analysis included: optimization of equilibrium geometry of phenanthridine in its first excited S_1 singlet state and computations of the frequencies of vibrational fundamental modes together with their geometry changes between the excited and the ground state. Comparison of the results of calculations with experimental data revealed their good agreement and an increase in the vibrational activity in the fluorescence spectrum in comparison to fluorescence spectrum of phenanthrene molecule (which is a parent aromatic hydrocarbon of phenanthridine and of 7,8-benzoquinoline). Such an increase in vibrational activity in the fluorescence spectrum was earlier observed also for 7,8-benzoquinoline molecule. Present analysis shows that this effect is due to molecular symmetry reduction caused by the substitution of nitrogen atom into the aromatic rings system of phenanthrene, as well as to the changes of equilibrium structure between the ground and excited states.

9

Experimental and Theoretical Spectroscopic Studies on Selected Igepals

80%

Pasterna G., Kupka T., Wrzalik R., Pasterny K., Blicharski J. S.

Acta Physica Polonica A

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2000

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vol. 98

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issue 5

651-654

EN

Several nonionic igepals characterized by the formula (C_{m}H_{2m+1})-C_{6}H_{4} (OCH_{2}CH_{2})_{n}OH were investigated by high resolution NMR and IR spectroscopy. Gauge invariant atomic orbital density functional theory NMR calculations on model molecules in the gas phase additionally supported the assignment of experimental carbon signals. Different orientations of individual sub-units of an aliphatic chain relative to external magnetic field and trans-gauche transitions were assumed to explain complex patterns of carbon spectra in the aliphatic region of igepals with linear alkyl chain.

10

High-lying doubly excited states of He and H−: electron correlations and classification schemes

70%

Themelis S.

Open Physics

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2005

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vol. 3

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issue 3

324-338

EN

High-lying doubly excited states of He and H− are studied and energies and intrinsic characteristics of their wave-functions are reported. Results for energies of 3Po and 1D doubly excited states associated with the hydrogenic thresholds up to N = 20 are presented and compared to available data from the literature. The classification of these doubly excited states by approximate quantum numbers is reexamined.

11

Large scale multi-configuration Hartree-Fock calculation of the hyperfine structure of the ground state of vanadium

61%

Scharf O., Gaigalas G.

Open Physics

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2006

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vol. 4

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issue 1

42-57

EN

The hyperfine structure of the ground state of vanadium, 51VI, is calculated in the nonrelativistic framework of the multi-configuration Hartree-Fock approximation. A configuration state function limiting algorithm is used to make the calculations feasible and to study the influence of core, valence and core-valence correlations in detail. The obtained configuration state function space captures the most important orbital correlations within 2%. Further correlations are included through configuration interaction calculation. The atomic state functions are used to evaluate the magnetic dipole hyperfine factor A and the electric quadrupole factor B. It turns out that the ab initio calculation can not capture the core polarization of the 2s shell. It introduces an error that is higher than the Hartree-Fock approximation. However, the detailed correlations being observed suggest the introduction of a wrong correlation orbital due to the algorithm being used. Neglecting this orbital leads to good agreement with 2% deviation from the experimental values for the A factors.

12

Influence of Local Environment on the Electronic Structure and Magnetic Properties of Ni_{1-x}Cu_{x}MnSb Alloys

61%

Jezierski A., Szytuła A.

Acta Physica Polonica A

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2000

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vol. 97

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issue 3

607-610

EN

The magnetic ordering in Ni_{1-x}Cu_{x}MnSb alloys changes from ferromagnetic (x=0) to antiferromagnetic (x=1). The X-ray and neutron diffraction showed that the systems crystallise in C1_{b} type structure. We present an influence of the local chemical ordering on the electronic and magnetic properties of Ni_{1-x}Cu_{x}MnSb alloys. The band structure and the magnetic moments were calculated by the spin-polarised linear muffin-tin orbital in the atomic sphere approximation method for the experimental values of the lattice parameters. The magnetic moment of Mn increases from 3.8 μ_{B} for x=0 to 4.18 μ_{B} for x=1.

13

Towards relativistic ECP / DFT description of chemical bonding in E112 compounds: spin-orbit and correlation effects in E112X versus HgX (X=H, Au)

51%

Zaitsevskii A., Rykova E., Mosyagin N., Titov A.

Open Physics

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2006

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vol. 4

|

issue 4

448-460

EN

The relativistic effective core potential (RECP) approach combined with the spin-orbit DFT electron correlation treatment was applied to the study of the bonding of eka-mercury (E112) and mercury with hydrogen and gold atoms. Highly accurate small-core shape-consistent RECPs derived from Hartree-Fock-Dirac-Breit atomic calculations with Fermi nuclear model were employed. The accuracy of the DFT correlation treatment was checked by comparing the results in the scalar-relativistic (spin-orbit-free) limit with those of high level scalar-relativistic correlation calculations within the same RECP model. E112H was predicted to be slightly more stable than its lighter homologue (HgH). The E112-Au bond energy is expected to be ca. 25–30 % weaker than that of Hg-Au. The role of correlations and magnetic (spin-dependent) interactions in E112-X and Hg-X (X=H, Au) bonding is discussed. The present computational procedure can be readily applied to much larger systems and seems to be a promising tool for simulating E112 adsorption on metal surfaces.

14

Spectral Investigations of Fullerene-Porphyrin Complexes

51%

Barszcz B., Bogucki A., Laskowska B., Ion R., Graja A.

Acta Physica Polonica A

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2007

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vol. 112

|

issue S

S-143-S-152

EN

Spectral investigations of someμ-oxo-dimer complexes of trivalent metals (Mn, Fe) with two different ligands: tetraphenylporphyrin and tetranaphthylporphyrin (TNP), and fullerene (C_{60} and C_{70}) complexes withμ-oxobis[5,10,15,20-tetraarylporphyrinatometal (III)] (TXP-M)_2O dimer, where M = Fe, Mn and X = phenyl or naphthyl, are presented. Discussion of the main electronic and vibrational bands observed in the UV-Vis-IR and Raman spectra of both classes of fullerene-porphyrin systems is given. Experimental data are completed with the quantum chemical calculations of MnTNP^+ component.

15

Electric Dipole Moments of Acetone and of Acetic Acid Measured in Supersonic Expansion

51%

Dorosh O., Kisiel Z.

Acta Physica Polonica A

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2007

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vol. 112

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issue S

S-95-S-104

EN

Precise values for electric dipole moments of isolated acetone and acetic acid molecules were determined from the Stark effect measurements made on lowest J rotational transitions at conditions of supersonic expansion. The new results areμ_{tot} =μ_b =2.9345(22) D for acetone from measurements on the 1_{11}← 1_{01} transition, andμ_a =0.8631(8),μ_b =1.4345(11),μ_{tot} =1.6741(10) D for acetic acid, from measurements on 1_{11}← 0_{00} and 1_{01}←0_{00} transitions. A comparison with previous determinations and with results of quantum chemical calculations is presented.

Refine search results

Spectroscopy and Photophysics of Monoazaphenanthrenes II. Ab initio Analysis of Molecular Parameters and Electronic Spectra

Natural Bond Orbital (NBO) Population Analysis of 1-Azanapthalene-8-ol

Fluorescence Spectra of 7,8-Benzoquinoline Isolated in the Supersonic Jet Expansion - An Ab Initio Analysis

Spectroscopy of 2-aminopurine: An MCSCF Study

Resonant Spin Splitting in III-V Semiconductors

The Semiempirical Method for Finding Thermal Characteristics of Simple Crystals

Molecular Modelling of Interface Occurrence of Ti (C,N,O) - Fe Composite

Fluorescence Spectra of Phenanthridine Isolated in the Supersonic Jet Expansion - An Ab Initio Analysis

Experimental and Theoretical Spectroscopic Studies on Selected Igepals

High-lying doubly excited states of He and H−: electron correlations and classification schemes

Large scale multi-configuration Hartree-Fock calculation of the hyperfine structure of the ground state of vanadium

Influence of Local Environment on the Electronic Structure and Magnetic Properties of Ni_{1-x}Cu_{x}MnSb Alloys

Towards relativistic ECP / DFT description of chemical bonding in E112 compounds: spin-orbit and correlation effects in E112X versus HgX (X=H, Au)

Spectral Investigations of Fullerene-Porphyrin Complexes

Electric Dipole Moments of Acetone and of Acetic Acid Measured in Supersonic Expansion