scholarly journals Applications of Hückel-Su-Schrieffer-Heeger method

2021 ◽  
Author(s):  
Jan H. Kwapisz ◽  
Leszek Z. Stolarczyk
Keyword(s):  
Geometry Optimization ◽  
Attractive Alternative ◽  
X Rays ◽  
Modular Architecture ◽  
Excitation Spectra ◽  
Bond Lengths ◽  
Simple Quantum ◽  
Quantum Approach ◽  
Polycyclic Aromatic ◽  
Electronic Ground

AbstractThe equilibrium carbon-carbon (C-C) bond lengths in π-electron hydrocarbons are very sensitive to the electronic ground-state characteristic. In the recent two papers by Stolarczyk and Krygowski (J Phys Org Chem, 34:e4154,e4153, 2021) a simple quantum approach, the Augmented Hückel Molecular Orbital (AugHMO) model, is proposed for the qualitative, as well as quantitative, study of this phenomenon. The simplest realization of the AugHMO model is the Hückel-Su-Schrieffer-Heeger (HSSH) method, in which the resonance integral β of the HMO model is a linear function the bond length. In the present paper, the HSSH method is applied in a study of C-C bond lengths in a set of 34 selected polycyclic aromatic hydrocarbons (PAHs). This is exactly the set of molecules analyzed by Riegel and Müllen (J Phys Org Chem, 23:315, 2010) in the context of their electronic-excitation spectra. These PAHs have been obtained by chemical synthesis, but in most cases no diffraction data (by X-rays or neutrons) of sufficient quality is available to provide us with their geometry. On the other hand, these PAHs are rather big (up to 96 carbon atoms), and ab initio methods of quantum chemistry are too expensive for a reliable geometry optimization. That makes the HSSH method a very attractive alternative. Our HSSH calculations uncover a modular architecture of certain classes of PAHs. For the studied molecules (and their fragments – modules), we calculate the values of the aromaticity index HOMA.

Molecular orbital structures of sulfones

1982 ◽  
Vol 60 (6) ◽  
pp. 730-734 ◽  
Author(s):  
Russell J. Boyd ◽  
Jeffrey P. Szabo
Keyword(s):  
Crystal Structure ◽  
Gas Phase ◽  
Molecular Orbital ◽  
Geometry Optimization ◽  
Membered Ring ◽  
Molecular Orbital Calculations ◽  
Bond Lengths ◽  
Comparison With Experiment ◽  
The Difference

Abinitio molecular orbital calculations are reported for several cyclic and acyclic sulfones. The geometries of XSO2Y, where X, Y = H, F, or CH3 are optimized at the STO-3G* level. Similar calculations are reported for the smallest cyclic sulfone, thiirane-1,1 -dioxide, as well as the corresponding sulfoxide, thiirane-1-oxide, and the parent sulfide, thiirane. Where comparison with experiment is possible, the agreement is satisfactory. In order to consider the possibility of substantial differences between axial and equatorial S—O bonds in the gas phase, as observed in the crystal structure of 5H,8H-dibenzo[d,f][1,2]-dithiocin-1,1-dioxide, STO-3G* calculations are reported for a six-membered ring, thiane-1,1-dioxide, and a model eight-membered ring. Limited geometry optimization of the axial and equatorial S—O bonds in the chair conformations of the six- and eight-membered rings leads to bond lengths of 1.46 Å with the difference being less than 0.01 Å.

Excitation Spectra of Large Jet-Cooled Polycyclic Aromatic Hydrocarbon Radicals: 9-Anthracenylmethyl (C15H11) and 1-Pyrenylmethyl (C17H11)

2013 ◽  
Vol 117 (50) ◽  
pp. 13899-13907 ◽  
Author(s):  
Gerard D. O’Connor ◽  
George B. Bacskay ◽  
Gabrielle V. G. Woodhouse ◽  
Tyler P. Troy ◽  
Klaas Nauta ◽  
...  
Keyword(s):  
Polycyclic Aromatic Hydrocarbon ◽  
Aromatic Hydrocarbon ◽  
Excitation Spectra ◽  
Polycyclic Aromatic ◽  
Hydrocarbon Radicals

An Introduction to Low Energy X-Ray and Electron Analysis

1969 ◽  
Vol 13 ◽  
pp. 1-25 ◽  
Author(s):  
Burton L. Henke
Keyword(s):  
Electron Spectroscopy ◽  
Auger Electron ◽  
Light Element ◽  
Low Energy ◽  
X Rays ◽  
Excitation Spectra ◽  
X Ray ◽  
Langmuir Blodgett ◽  
Electrostatic Analyzer ◽  
Introductory Review

This is an introductory review of the physics and applications of low energy x-rays and electrons in the 10-1000 ev region. The basic interactions of these radiations within matter are discussed and typical de-excitation spectra, fluorescent x-ray and photoAuger electron, are presented. Specific examples of spectrographic methods and instruments for the low energy region are described as “based upon the use of long-spaced, Langmuir-Blodgett type of multilayers for ultrasoft x-ray analysis and the use of the hemispherical electrostatic analyzer for photo-Auger electron spectroscopy. Some examples of spectrographic signal, signal/background, and resolution are presented for applications to light element fluorescence, valence emission band, and photo-Auger electron analysis. The special aspects of the low energy x-ray analysis of high temperature plasmas and of x-ray astronomical sources in general are described.

Internal, translational, and angular momentum product state distributions of CuF molecules desorbing associatively from copper surfaces

1994 ◽  
Vol 72 (3) ◽  
pp. 643-651 ◽  
Author(s):  
A. Bracker ◽  
P. Jakob ◽  
U. Näher ◽  
M. Rüdiger ◽  
K. Sugawara ◽  
...  
Keyword(s):  
Angular Momentum ◽  
Polycrystalline Sample ◽  
Copper Surface ◽  
Degree Of Polarization ◽  
Product State ◽  
Excitation Spectra ◽  
Copper Surfaces ◽  
Isotropic Distribution ◽  
Electronic Ground ◽  
Translational Product

The dry etching reaction of solid copper surfaces with fluorine atoms or molecules has been studied with laser-induced fluorescence spectroscopy. The reaction product, copper monofluoride, CuF, is produced in the X1Σ+ electronic ground state and desorbs into the gas phase at surface temperatures above approximately 750 K. Rotationally resolved LIF excitation spectra of the C1П ← X1Σ+ band system of CuF molecules desorbing from an isotopically purified 63Cu polycrystalline sample are obtained under conditions of coherent saturation. From the product state analysis it is deduced that the rovibrational product populations are in thermal equilibrium with the surface. The same holds for the translational velocity distribution obtained by Doppler-shift measurements. A pronounced polarization effect, particularly strong for Q branch transitions, can be traced back to photoselection of single-parity levels in the Λ doublets of the C1П state. A theoretical analysis for the distribution of J vectors, based on the formalism of Greene and Zare, shows that the measured degree of polarization is quantitatively in agreement with an isotropic distribution of rotational angular momentum vectors. The vibrational and translational product equilibration is not affected by changing the reactants from F2 molecules to F atoms, which increases the exoergicity of the overall reaction. The results are interpreted in terms of the absence of a barrier for desorption and a long residence time of the chemisorbed CuF molecules at the copper surface. The lack of any translational and rotational cooling is discussed within the framework of a model.

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