Semi-empirical pertci ionization spectra of some cumulenes and cumulene-like systems. Low-energy non-koopmans' ionizations

1986 ◽  
Vol 103 (2-3) ◽  
pp. 375-382 ◽  
Author(s):  
Armin Schweig ◽  
Werner Zittlau
Keyword(s):  
Low Energy ◽  
Semi Empirical

Investigation of the attenuation of the fluxes of the low-energy plasma component of electric rocket engines by the ventilation holes of the unpressurized instrument compartment of the spacecraft

2021 ◽  
Author(s):  
I.A. Maximov ◽  
A.B. Nadiradze ◽  
R.R. Rakhmatullin ◽  
V.A. Smirnov ◽  
R.E. Tikhomirov ◽  
...  
Keyword(s):  
Electric Propulsion ◽  
Plasma Source ◽  
Low Energy ◽  
Rocket Engines ◽  
Plasma Component ◽  
Plasma Flows ◽  
Energy Component ◽  
Honeycomb Filler ◽  
Semi Empirical ◽  
Made In

The results of an experimental study of the attenuation of the fluxes of the low-energy component of the plasma formed during the operation of electric propulsion engines (ERE), ventilation holes (VH) of the non-sealed equipment compartment (NSEC) of the spacecraft (SC) are presented. Authors studied the attenuation of plasma fluxes by standard VHs made in honeycomb panels that form the NSEC. A Hall-effect engine of the SPT-70 type was used as a plasma source. The experiment consisted of measuring the plasma concentration at the inlet and outlet of the VH. The concentration at the inlet was measured with a flat Langmuir probe, and at the outlet with a Faraday probe, which allows collecting all ions passing through the VH. The aim of the work was to study the weakening of the fluxes of the lowenergy component of the EJE plasma when passing through the VH in the honeycomb-nels that form the NSEC. Based on the experimental data, a semi-empirical model was constructed that describes the dependence of the attenuation coefficient of plasma flows on the geometric parameters of the vent-holes. It has been established that a vent-holes of this design attenuates the plasma flows by 102 ... 104 times. The largest contribution to the weakening of plasma fluxes is made by the honeycomb filler, which is due to the recombination of ions during their collision with the channel walls. Taking into account the attenuation of the fluxes of the low-energy component of the plasma of electric rocket engines by ventilation holes is a key stage in assessing the effect of plasma on the power on-board equipment of spacecraft and should be used by spacecraft developers when analyzing the resistance to this factor.

scholarly journals THE SYNTHESIS OF 1,3-DIMETHYL-6,7-DIMETHOXY-3,4-DIHYDROISOQUINOLINE FROM METHYLEUGENOL : APPLICATION OF RITTER REACTION FOR DIRECTLY CYCLIZATION

2010 ◽  
Vol 6 (3) ◽  
pp. 286-291 ◽  
Author(s):  
M. Farid Rahman ◽  
Elvina Dhiaul Iftitah
Keyword(s):  
Sulphuric Acid ◽  
Room Temperature ◽  
Acid Catalyst ◽  
Empirical Method ◽  
Low Energy ◽  
Ritter Reaction ◽  
Experimental Laboratory ◽  
Semi Empirical

The synthesis of 1,3-dimethyl-6,7-dimethoxy-3,4-dihydroisoquinoline from methyleugenol with application of Ritter reaction for directly cyclization was presented. This research was carried out in 2 steps : (1) Determination of intermediate stability that undergo in the reaction by using hyperchem version 6 with AM 1 semi empirical method, and (2) Synthesis of dihydroisoquinoline from methyleugenol and acetonitrile with acid catalyst (H2SO4) in the laboratory. The result of AM 1 calculation found that generally, the intermediate encourage the formation dihydroisoquinoline product, had low energy were compared with the intermediate in other product. Therefore, the dihydroisoquinoline product was easily formed. The result of experimental laboratory found that dihydroisoquinoline could be synthesed from methyleugenol and acetonitrile in the presence sulphuric acid under reflux in 74,92% yields. In despite, the minor product was formed with amount 6,74%. While the reaction at room temperature gave dihydroisoquinoline in poor yield about 11,42%.   Keywords: stability of intermediate, dihydroisoquinoline, Ritter reaction

scholarly journals Effect of Unwanted Guest Molecules on the Stacking Configuration of Covalent Organic Frameworks: A Periodic Energy Decomposition Analysis

2020 ◽  
Author(s):  
A.D. Dinga Wonanke ◽  
Mathew Addicoat
Keyword(s):  
Guest Molecule ◽  
Dispersion Model ◽  
Critical Role ◽  
Decomposition Analysis ◽  
Empirical Method ◽  
Low Energy ◽  
Energy Decomposition Analysis ◽  
Energy Decomposition ◽  
Guest Molecules ◽  
Semi Empirical

Elucidating the precise stacking configuration of a covalent organic framework, COF, is critical to fully understand their various applications. Unfortunately, most COFs form powder crystals whose atomic characterisations are possible only through powder X-ray diffraction (PXRD) analysis. However, this analysis has to be coupled with computational simulations, wherein computed PXRD patterns for different stacking configurations are compared with experimental patterns to predict the precise stacking configuration. This task is often computationally challenging firstly because, computation of these systems mostly rely on the use of semi-empirical methods that need to be adequately parametrised for the system being studied and secondly because some of these compounds possess guest molecules, which are not often taken into account during computation. COF-1 is an extreme case in which the presence of the guest molecule plays a critical role in predicting the precise stacking configuration. Using this as a case study, we mapped out a full PES for the stacking configuration in the guest free and guest containing system using the GFN-xTB semi-empirical method followed by a periodic energy decomposition analysis using first principle DFT. Our results showed that the presence of the guest molecule leads to multiple low energy stacking configurations with significantly different lateral offsets. Also, the semi-empirical method does not precisely predict DFT low energy configurations, however, it accurately accounts for dispersion. Finally, our quantum-mechanical analysis demonstrates that electrostatic-dispersion model suggested Hunter and Sanders accurately describe the stacking in 2D COFs as oppose to the newly suggested Pauli-dispersion model.

FULLERENE DERIVATIVES: STRUCTURES AND STABILITIES OF C60O AND C70O

1992 ◽  
Vol 06 (23n24) ◽  
pp. 3821-3831 ◽  
Author(s):  
KRISHNAN RAGHAVACHARI
Keyword(s):  
Oxygen Atom ◽  
Infrared Spectra ◽  
Ground State ◽  
Membered Ring ◽  
Low Energy ◽  
Fullerene Derivatives ◽  
Hartree Fock ◽  
Semi Empirical ◽  
Very High ◽  
C Nmr

Semi-empirical (MNDO) and ab-initio Hartree-Fock (3–21G) calculations on the structures and stabilities of C 60 O and C 70 O are reported. Two low energy isomers of C 60 O , formed by an oxygen atom bridging the two different C–C bonds in C 60, have been found. The first isomer has an epoxide structure with a bridging oxygen across the bond between two fused six-membered rings in C 60 (bridging C–C≈1.6 Å). Its 13 C NMR and infrared spectra are consistent with those seen for the experimentally isolated form of C 60 O . However, the second isomer containing a bridging oxygen across the bond between a five- and a six-membered ring is slightly more stable and appears to be the ground state of C 60 O . The bridging C–C bond opens out to a distance of ≈2.1 Å in this isomer. Endohedral isomers of C 60 O are calculated to be very high in energy. For C 70 O , we have characterized eight isomers formed by an oxygen atom bridging each of the eight distinct C–C bonds in C 70. The ground state isomer corresponds to oxygen bridging across an equatorial C–C bond in C 70 which opens out to a distance of ≈2.2 Å. This structure is different from the bridged paracyclene-like isomer proposed previously for C 70 O . Comparison is made between C 60 O and C 70 O .

A semi-empirical approach for determination of low-energy gamma-emmiters in sediment samples with coaxial Ge-detectors

2004 ◽  
Vol 61 (2-3) ◽  
pp. 361-366 ◽  
Author(s):  
E.G San Miguel ◽  
J.P Perez-Moreno ◽  
J.P Bolivar ◽  
R Garcı́a-Tenorio
Keyword(s):  
Empirical Approach ◽  
Low Energy ◽  
Sediment Samples ◽  
Energy Gamma ◽  
Semi Empirical

scholarly journals Methodological Investigation for Hydrogen Addition to Small Cage Carbon Fullerenes

Crystals ◽  
2021 ◽  
Vol 11 (11) ◽  
pp. 1334
Author(s):  
Yuri Tanuma ◽  
Toru Maekawa ◽  
Chris Ewels
Keyword(s):  
Computational Cost ◽  
Low Energy ◽  
Brute Force ◽  
Empirical Methods ◽  
Systematic Testing ◽  
Hydrogen Addition ◽  
Stable Species ◽  
Local Electronic Structure ◽  
Computational Identification ◽  
Semi Empirical

Hydrogenated small fullerenes (Cn, n < 60) are of interest as potential astrochemical species, and as intermediates in hydrogen-catalysed fullerene growth. However, the computational identification of key stable species is difficult due to the vast configurationally space of structures. In this study, we explored routes to predict stable hydrogenated small fullerenes. We showed that neither local fullerene geometry nor local electronic structure analysis was able to correctly predict subsequent low-energy hydrogenation sites, and sequential stable addition searches also sometimes failed to identify most stable hydrogenated fullerene isomers. Of the empirical and semi-empirical methods tested, GFN2-xTB consistently gave highly accurate energy correlations (r > 0.99) to full DFT-LDA calculations at a fraction of the computational cost. This allowed identification of the most stable hydrogenated fullerenes up to 4H for four fullerenes, namely two isomers of C28 and C40, via “brute force” systematic testing of all symmetry-inequivalent combinations. The approach shows promise for wider systematic studies of smaller hydrogenated fullerenes.

Sign in / Sign up

Export Citation Format

Share Document