Global Electron Density Research Articles

Modeling the global ionospheric electron densities based on the EOF decomposition of the ionospheric radio occultation observation

An attempt is made to model the three-dimensional global structures and temporal variations of the ionospheric electron density (Ne) using the radio occultation (RO) Ne profile data obtained by the COSMIC/FORMOSAT-3, CHAMP and GRACE missions during the period from July 2006 to June 2017. The modeling technique we adopted is based on the empirical orthogonal function (EOF) analysis of the RO Ne dataset which is binned with grids of 2.5° in geomagnetic latitudes and 1/3 hr in geomagnetic local time (equivalent to 5° in geomagnetic longitudes) and 10 km in height. The EOF analysis decomposed the binned (gridded) Ne dataset into a series of eigen modes or basis functions (E i ) representing the variations with geomagnetic latitude, geomagnetic local time as well as height and the associated EOF amplitude coefficients (A i ) representing the variations with seasons as well as solar cycle activity. Our results showed that the EOF components (E i , A i ) obtained by the EOF decomposition have different three-dimensional spatial structures with distinct features attributable to different factors or processes controlling the variations of the ionosphere: the first EOF component represents mainly the global mean structure of Ne and its temporal variation with seasons and solar cycle activity; the second EOF component represents mainly the seasonal control of the solar zenith angle on the ionosphere; the third EOF component is representative of the uplifting or lowering of the peak height where Ne reaches its maximum value; the fourth and fifth EOF components represent respectively the variations of the thickness of the ionosphere in the southern and northern hemispheres. It is found that the obtained eigen series converges quickly, with the first five EOF components contributing as high as 98% of the variances of the Ne dataset. We then modeled the EOF coefficients A i obtained by the EOF decomposition using the harmonic functions representing the annual and semi-annual variations, with the solar cycle dependences being taken into account by including the changes of the harmonic amplitudes with the solar irradiance flux index F10.7. The Ne model is constructed using the A i thus modeled and E i obtained by the EOF decomposition. Comparison between the Ne model output results and the COSMIC-2 observational data showed that the modeled results capture well the global structures of the observational data and the model output results have very high linear correlation coefficients with the observational ones (R > 0.9), justifying the modeling technique used in our present study.

Observing System Impact on Ionospheric Specification Over China Using EnKF Assimilation

AbstractAccurate ionospheric specification for the current and future is one of the key tasks in operational space weather. In this work, we have assessed the effect of a dense ground network consisting of different radio instruments either developed or under developing on ionosphere nowcasting and forecasting over China and adjacent region (0–60°N and 70–140°E) through observing system simulation experiments. The data assimilation system is an Ensemble Kalman filter (EnKF) ionosphere and thermosphere data assimilation algorithm. The National Center for Atmospheric Research Thermosphere Ionosphere Electrodynamics General Circulation Model is used as a background model. Effects of different observation types, including the slant total electron content from Beidou System geostationary satellite and Global Position System and electron density observations from ionosondes and incoherent scattering radar on the ionospheric nowcasting and forecasting, are examined by the accurate specification of ionosphere key parameters (total electron content and 3‐D electron density). We found that simultaneously assimilating different observation types can greatly improve the quality of ionosphere specification. Furthermore, updating the thermospheric state variables in the coupled thermosphere‐ionosphere forecast model in the assimilation step plays an important role in improving the ionosphere forecasting. The ionosphere forecasting capability can last longer (>24 hr) in each observing system simulation experiment due to the adjusted thermosphere states. This study can provide a reference for observing system design over the China region and future ionosphere forecasting operation.

Unveiling the mechanism and selectivity of [3+2] cycloaddition reactions of benzonitrile oxide to ethyl trans-cinnamate, ethyl crotonate and trans-2-penten-1-ol through DFT analysis

The mechanism and regioselectivity of [3+2] cycloaddition (32CA) reactions of benzonitrile oxide with ethyl trans-cinnamate, ethyl crotonate and trans-2-penten-1-ol has been studied in gas phase and in acetonitrile, ethyl acetate and tetrahydrofuran using the B3LYP functional in connection with 6-31G(d) basis set. The 32CA reactions followed one-step mechanism with asynchronous TSs. The calculated global electron density transfer (GEDT) at the TSs showed electronic flux from benzonitrile oxide to ethyl trans-cinnamate and ethyl crotonate, while the electronic flux from trans-2-penten-1-ol to benzonitrile oxide was predicted, in complete agreement with the Conceptual Density Functional Theory (CDFT) indices. The regioselectivity is correctly described in coherence with the experiment data. The intermolecular interaction at the TSs was realized through visualization and quantification by means of independent gradient model (IGM) analysis based on promolecular density.

Unravelling the regio- and stereoselective synthesis of bicyclic N,O-nucleoside analogues within the molecular electron density theory perspective.

The [3 + 2] cycloaddition (32CA) reactions of 1-pyrroline-1-oxide with N-vinyl nucleobases leading to bicyclic N,O nucleoside analogues have been studied within the molecular electron density theory (MEDT) at the MPWB1K/6-311G(d,p) computational level. These non-polar zwitterionic type 32CA reactions take place through a one-step mechanism with minimal global electron density transfer (GEDT) at the TSs and the exo/ortho approach mode as the energetically favoured reaction path. The 32CA reactions of N-vinyl nucleobases with thymine and cytosine substituents respectively show the activation enthalpies of 15.2 and 12.5 kcal mol−1 in toluene. The reactions are irreversible due to strong exothermic character of − 35.4–− 26.4 kcal mol−1 in toluene. The bonding evolution theory (BET) study suggests that these 32CA reactions take place through the coupling of pseudoradical centres with earlier C–C bond formation and the formation of new C–C and C–O covalent bonds has not been started in the TSs. Non-covalent interactions (NCI) are predicted at the TSs from the visualization of NCI gradient isosurfaces.Electronic supplementary materialThe online version of this article (10.1007/s11224-020-01569-x) contains supplementary material, which is available to authorized users.

Comparison and evaluation of a bottom-up GPS-RO electron density retrieval for D and E regions using radar observations and models

The lack of reliable global E-region electron density or conductivity measurements has hampered a detailed and quantitative understanding of the E-region electrodynamic processes. The characterization of the global E-region ionospheric irregularities as a function of local time, longitude, and season remains a great challenge. In this study, we evaluate the electron densities retrieved by Wu (2018) in the D and E regions using ground-based radar data and empirical models. Unlike in the conventional top-down retrieval methodology, the new approach avoids the Abel weighting function that carries substantial sensitivity to the electron density residuals from the F-region even after they have been corrected. The new technique uses a bottom-up approach in which the F-region contributions in the excess phase are more effectively removed compared to the Abel inversion, and hence more accurate electron density retrievals in D and E regions are determined. The results are compared and evaluated with two low and mid-latitude incoherent scatter radar observations — the Arecibo Observatory’s 430 MHz radar, located in Puerto Rico (18∘N, 67∘W) and the Millstone Hill Observatory’s 440 MHz radar, located in Massachusetts (42∘N, 72∘W). In addition, the results are also compared with two models — the International Reference Ionosphere model (IRI-2016) and the Faraday International Reference Ionosphere model (FIRI-2018) at these two locations. The comparison of electron density height profiles from GPS-RO retrievals at the two locations show good agreement with radar measurements, as well as the FIRI-2018 model predictions, especially at ∼ 85–100 km. The seasonal and diurnal climatology comparisons of GPS-RO retrieved electron density show good agreement with radar observations at both locations, and also reflect the influence of the solar cycle on E-region electron density. It is noticed that the GPS-RO background electron density at Millstone Hill increases by ∼ 20% at around 105 km from solar minimum to the maximum during cycle 24 which is in agreement with radar observations and FIRI-2018 model predictions.

Unveiling the Lewis Acid Catalyzed Diels-Alder Reactions Through the Molecular Electron Density Theory.

The effects of metal-based Lewis acid (LA) catalysts on the reaction rate and regioselectivity in polar Diels–Alder (P-DA) reactions has been analyzed within the molecular electron density theory (MEDT). A clear linear correlation between the reduction of the activation energies and the increase of the polar character of the reactions measured by analysis of the global electron density transfer at the corresponding transition state structures (TS) is found, a behavior easily predictable by analysis of the electrophilicity ω and nucleophilicity N indices of the reagents. The presence of a strong electron-releasing group in the diene changes the mechanism of these P-DA reactions from a two-stage one-step to a two-step one via formation of a zwitterionic intermediate. However, this change in the reaction mechanism does not have any chemical relevance. This MEDT study makes it possible to establish that the more favorable nucleophilic/electrophilic interactions taking place at the TSs of LA catalyzed P-DA reactions are responsible for the high acceleration and complete regioselectivity experimentally observed.

A regio- and stereoselectivity and molecular mechanism study on the addition reactions of morpholine and m-CPBA to 9α-hydroxyparthenolide using DFT calculations

<p class="Mabstract"><span lang="EN-US">The chemoselectivity and stereospecificity of the addition of the morpholine and the meta-chloroperoxybenzoic acid</span><span lang="EN-US"> (</span><span lang="EN-US">m-CPBA) onto 9α-hydroxyparthenolide were studied using Density Functional Theory (DFT) calculations with the B3LYP/6-311+G(d,p) computational level within the Molecular Electron Density Theory (MEDT), to demonstrate the key role of the Global Electron Density Transfer (GEDT) and to examine the polar character of these reactions. This work is divided into two parts; the first part concerns the reaction between the morpholine and the 9α-hydroxyparthenolide. The second part deals with the epoxidation of the 9α-hydroxyparthenolide by m-CPBA followed by the addition of the morpholine to the major product resulting from the epoxidation step. The obtained results show that the reaction between the morpholine and the 9α-hydroxyparthenolide takes place on the double bond C<sub>3</sub>=C<sub>4</sub>. On the other hand, when 9α-hydroxyparthenolide is attacked by m-CPBA, the epoxidation reaction is carried out on the double bond C<sub>1</sub>=C<sub>2</sub>.</span></p>

A molecular electron density theory study to understand the interplay of theory and experiment in nitrone-enone cycloaddition

[3 + 2] cycloaddition (32CA) reaction of C,N-diaryl nitrone with benzylidene acetone has been studied to analyse the mechanism, selectivity and polar character of this nitrone-enone cycloaddition. Topological analysis of the electron localization function (ELF) shows the absence of pseudoradical and carbenoid centre in the nitrone, which allows its classification as a zwitter-ionic (zw) type three atom component (TAC) and hence participation in zw- type cycloadditions is associated with high activation energy barriers. This 32CA reaction follows a one-step mechanism with asynchronous TSs. Endo/meta product is obtained as the major cycloadduct experimentally, which can be rationalized from its calculated lowest activation energy among the four possible reaction pathways. Global electron density transfer (GEDT) at the TSs predict the non-polar character of this 32CA reaction. Topological analysis of the ELF and QTAIM parameters was performed at the TSs. Finally, non-covalent interaction (NCI) gradient isosurfaces are computed to obtain a visualization of non-covalent interactions at the interatomic bonding regions. The experimental and theoretical aspects of [3+2] cycloaddition reactions of C,N-diaryl nitrone with benzylidene acetone is described. The reaction is meta/endo selective and follows one step mechanism with non-covalent interactions. The C-C and C-O bonds are generated through coupling of pseudoradical centers.

Functionalization of the C20 fullerene by pyridine and pyrimidine: A theoretical study

A theoretical study at the levels of CAM-B3LYP and MP2 was reported, with the aim of understanding the possibility of functionalization of the C20 fullerene with pyridine and pyrimidine via a cycloaddition reaction. For this purpose, several [2+2] and [4+2] cycloaddition reactions were considered between C20 and pyridine or pyrimidine, and their thermodynamic and kinetic parameters were calculated. The results indicated that those [4+2] cycloaddition reactions are favorable ones in which the fullerene plays the role of a dienophile. It was also found that a [4+2] reaction path in which it takes place via the formation of two new C–C bonds between two fragments, C20 and heterocycle, is more favorable than that occurring via the formation of two different bonds, C-C and C–N. The calculation of global electron density transfer (GEDT) and molecular electrostatic potential (MESP) map revealed that the transition states are relatively polar and the C20 fullerene acts as an electron acceptor. Determination of Frontier Effective-for-Reaction Molecular Orbitals (FERMOs) relevant to pyridine and pyrimidine satisfactorily described the reactivity of different active sites of pyridine and pyrimidine. Finally, the calculation of the reactions synchronicity showed that the reactions are relatively synchronous.

Understanding the regio-and diastereoselective synthesis of a potent antinociceptive isoxazolidine from C-(pyridin-3-yl)-N-phenylnitrone in the light of molecular electron density theory

[3+2] cycloaddition reaction of C-(pyridin-3-yl)-N-phenylnitrone and 2-propen-1-ol yields stereochemically defined potent antinociceptive isoxazolidine derivative. Computational quantum calculations (CQC) are performed for this synthesis to predict the polar character, mechanism and selectivity within the framework of molecular electron density theory (MEDT). Topological analysis of the electron localization function (ELF) classifies the nitrone as a zwitter-ionic(zw-) type three atom component (TAC) showing absence of any pseudoradical or carbenoid centre. Four reaction channels corresponding to the possible regio- and stereoselective pathways are studied at DFT/ /B3LYP/6-311G(d,p) level of theory. The reaction follows one-step mechanism with asynchronous transition states and the computed activation energies agree well with experimental data. The reaction can be differentiated into nine ELF topological phases, with faster C?C bond formation. Global electron density theory (GEDT) at the favoured transition state and conceptual density functional theory (CDFT) indices at the ground state of the reagents indicate non-polar character. Non-covalent interactions are predicted by atoms-in-molecules (AIM) analysis and non-covalent interaction (NCI) plots at the transition states.

Characteristics of GNSS Total Electron Content Enhancements Over the Midlatitudes During a Geomagnetic Storm on 7 and 8 November 2004

AbstractThe characteristics of global electron density variations in the ionosphere during a geomagnetic storm on 7 and 8 November 2004 were investigated using total electron content (TEC) obtained from the global navigation satellite system (GNSS). The regions of enhanced TEC over North America, Europe, and Japan first appeared in the middle‐latitude regions. The TEC enhancements over North America showed a rapid longitudinal expansion and reached a wide longitudinal extent during the initial and main phases of the geomagnetic storm. TEC enhancements were simultaneously observed in both North America and Japan at 05:00 UT on 8 November. Observation data from the Defense Meteorological Satellite Program showed a slight enhancement of electron density at 850 km below the equatorward boundary of the middle‐latitude trough (45–48°N in geomagnetic latitude) over the Pacific Ocean. This electron density variation may correspond to the TEC enhancements observed in both Japan and North America. These results imply that an enhanced TEC region existed between North America and Japan. The TEC enhancement in Japan appeared with a magnetic conjugacy in the Southern Hemisphere, indicating one of the characteristics of storm‐enhanced density (SED). Moreover, TEC enhancements simultaneously appeared from Japan to central Asia at 11:00 UT on 8 November, corresponding to the early recovery phase of the geomagnetic storm. From the above results, it is suggested that SED phenomena can be simultaneously generated over a wide longitudinal width (~100°). The longitudinal extent of this SED event is 2.5–5.0 times longer than those reported by previous studies.

Exploring effects of the trifluoromethyl substituent on the chemoselectivity and regioselectivity of [3+2] cycloadditions of thiocarbonyl S‐methanides with α, β‐unsaturated ketones

AbstractA [3+2] cycloaddition (32CA) reaction between a thiocarbonyl ylide (TCY 2) and an electron‐deficient enone (TFB 3) in tetrahydrofuran (THF) was studied in the light of molecular electron density theory at the DFT‐B3LYP/6‐31G(d) computational level to probe energetics and selectivities. The reaction was investigated in four competitive reaction paths associated with the CC and CO chemoselectivities in TFB 3. An analysis of the density functional theory‐based reactivity indices shows that TCY 2 is a strong nucleophile, and TFB 3 is also a strong electrophile. Although both C4─C5 and C6─O7 double bonds of TFB 3 can potentially be involved in 32CA reaction toward TCY 2, computed relative Gibbs free energies obviously demonstrate that C6─O7 involvement in a quite regioselective manner is entirely preferred over the C4─C5 one in an excellent agreement with the chemoselectivity and regioselectivity observed experimentally. Interestingly, such a chemoselectivity could not be rationalized through assessment of the electrophilic Parr functions calculated at the C4, C5, C6, and O7 centers of TFB 3. The global electron density transfer value, 0.31 e, calculated at the most energetically preferred transition state structure TS 1 involved within the C6─O7 chemoselective reaction channel demonstrates that this pseudodiradical type (pdr‐type) 32CA reaction has a notable polar character.

Unravelling the mechanism and the origin of the selectivity of the [3 + 2] cycloaddition reaction between electrophilic nitrone and nucleophilic alkene

In this paper, we have studied within the molecular electron density theory the mechanism and the origin of the selectivity of the [3 + 2] cycloaddition reaction between electrophilic nitrone 1 and nucleophilic alkene, indole 2, using DFT method at the B3LYP/6-31G(d) theoretical level. The obtained results clearly indicated that this reaction is characterised by an ortho regioselectivity and an exo stereoselectivity. Inclusion of the solvent effects does not modify the obtained gas-phase selectivities but slightly increase the activation energies. The analysis of the geometries of the transition states with bond order and global electron density transfer shows that this reaction takes place via a slightly asynchronous non-polar one-step mechanism. Analysis of the electronic structure of nitrone 1 indicates that this species has a zwitterionic-type structure that enables its participation in zw-type 32CA reactions. Conceptual DFT reactivity indices analysis confirms the highly obtained activation energies and local Parr functions analysis allows us to explain the ortho regioselectivity of this 32CA reaction. NCI, ESP and QTAIM analyses indicate that the presence of several conventional and non-conventional interactions at the structure of the most favourable approach ortho–exo is the origin for the selectivity of this 32CA reaction.

Ionospheric Response to Disturbed Winds During the 29 October 2003 Geomagnetic Storm in the Brazilian Sector

AbstractModeling the ionosphere during disturbed periods is one of the most challenging tasks due to the complexity of the phenomena that affect the electric fields and the whole thermosphere environment. It is well known that both, prompt penetration electric fields and large amounts of energy deposited in the polar region during disturbed periods, produce significant disturbances in the global electron density distribution, in particular, in the equatorial ionization anomaly development. Besides, the disturbance dynamo, traveling atmospheric disturbances, and traveling ionospheric disturbances also affect the equatorial ionization anomaly density distribution. In this work we use the Sheffield University Plasmasphere‐Ionosphere Model at Instituto Nacional de Pesquisas Espaciais, to simulate the drastic effects that were observed at the low‐latitude ionosphere in the Brazilian region during a very intense magnetic storm event, the so‐called 2003 Halloween storms. In the absence of measured vertical drift during the storm, a new vertical drift deduced from the interplanetary electric field combined with the time variation of the F region virtual height is used as input. The simulation results showed that, in the case of the disturbed thermospheric wind, the ionospheric observations are better explained when a novel traveling wave‐like disturbance propagating from north to south, at a velocity equal to 300 m/s, is considered.

X-ray constrained spin-coupled technique: theoretical details and further assessment of the method.

One of the well-established methods of modern quantum crystallography is undoubtedly the X-ray constrained wavefunction (XCW) approach, a technique that enables the determination of wavefunctions which not only minimize the energy of the system under examination, but also reproduce experimental X-ray diffraction data within the limit of the experimental errors. Initially proposed in the framework of the Hartree-Fock method, the strategy has been gradually extended to other techniques of quantum chemistry, but always remaining limited to a single-determinant ansatz for the wavefunction to extract. This limitation has been recently overcome through the development of the novel X-ray constrained spin-coupled (XCSC) approach [Genoni et al. (2018). Chem. Eur. J. 24, 15507-15511] which merges the XCW philosophy with the traditional spin-coupled strategy of valence bond theory. The main advantage of this new technique is the possibility of extracting traditional chemical descriptors (e.g. resonance structure weights) compatible with the experimental diffraction measurements, without the need to introduce information a priori or perform analyses a posteriori. This paper provides a detailed theoretical derivation of the fundamental equations at the basis of the XCSC method and also introduces a further advancement of its original version, mainly consisting in the use of molecular orbitals resulting from XCW calculations at the Hartree-Fock level to describe the inactive electrons in the XCSC computations. Furthermore, extensive test calculations, which have been performed by exploiting high-resolution X-ray diffraction data for salicylic acid and by adopting different basis sets, are presented and discussed. The computational tests have shown that the new technique does not suffer from particular convergence problems. Moreover, all the XCSC calculations provided resonance structure weights, spin-coupled orbitals and global electron densities slightly different from those resulting from the corresponding unconstrained computations. These discrepancies can be ascribed to the capability of the novel strategy to capture the information intrinsically contained in the experimental data used as external constraints.

Ga-doped phagraphene as a superior media for sensing of carbon monoxide: A detailed theoretical investigation

Abstract The adsorption of highly toxic carbon monoxide molecule (CO) on pristine, Al, Si, and Ga-doped phagraphene are studied using Density Functional Theory (DFT) calculations at M06-2X level of theory with 6-311G++ (d,p) basis set, to explore the potential abilities of phagraphene as an effective CO detection sensor. The full relaxed geometries of CO molecule, pristine and doped phagraphenes and related CO/pristine and doped-phagraphene complexes are specified and the variety parameters such as energy of Highest Occupied Molecular Orbital (E HOMO), energy of Lowest Unoccupied Molecular Orbital (ELUMO), gap energy (Eg), energy of adsorption (Ead), basis set superposition error (BSSE), gap energy alterations percent (%ΔEg), Global Electron Density Transfer (GEDT), energy of Fermi level (EF), work function (Φ), work function alterations percent (%ΔΦ), Density of States (DOS) patterns and Molecular Electrostatic Potential (MEP) profiles were calculated and analyzed. The results demonstrate that the CO molecule has a very poor physical adsorption on the pristine phagraphene. The calculated Ead value of CO/Si-doped phagraphene complex (−4.2043 kcal/mol) is moderate, however, the calculated %Eg value (+2.3498%) shows that Si-doped phagraphene has a low sensibility to CO molecule. The Ead calculations also indicate that the adsorption of CO molecule on Ga-doped phagraphene (Ead = −6.9653 kcal/mol) has the shorter recovery time compared with Al-doped phagraphene (Ead = −8.1450 kcal/mol). Therefore, Ga-doped phagraphene can be considered as an promising gas sensing platform for detecting CO molecule.

A molecular electron density theory study on the [3+2] cycloaddition reaction of 5,5-dimethyl-1-pyrroline N-oxide with 2-cyclopentenone

In the present work, the [3 + 2] cycloaddition reaction of 5,5-dimethyl-1-pyrroline N-oxide (Nit-5) and 2-cyclopentenone (CPN-6), experimentally reported by Tamura et al., was theoretically studied using the newly introduced molecular electron density theory (MEDT). Based on the experimental findings, this reaction takes place in an O3-C4 regio- and an exo-stereospecific fashion to give corresponding [3 + 2] exo cycloadduct as the sole product. The results of the potential energy surface analysis indicated that the experimentally reported product is more favorable both thermodynamically and kinetically relative to other possible adducts. In complete agreement with the experimental outcomes, the conceptual density functional theory reactivity indices explained the reactivity and regioselectivity of the reaction. Calculation of global electron density transfer of the energetically most preferred transition state indicated that the electron density fluxes from Nit-5 as a nucleophilic species toward CPN-6 as an electrophilic species. Analysis of the molecular electrostatic potential map of the most favorable transition state showed that approach of Nit-5 and CPN-6 locates the oppositely charged regions over each other leading to attractive forces between two reagents rationalizing the exo stereoselectivity predominance. The molecular mechanism of the reactions was specified using electron localization function analysis over some relevant points along the intrinsic reaction coordinate profile of the most favorable transition state and the results indicated that this zwitterionic-type [3 + 2] cycloaddition reaction proceeds through a two-stage one-step mechanism. In fact, while the O3-C4 single bond is initialy formed between two fragments through donation of some electron density from the O3 oxygen lone electron-pairs of Nit-5 toward the C4 carbon atom of CPN-6, the delayed C1-C5 single bond begins to form via C1- to -C5 coupling of pseudodiracal centers created on theses atoms over the course of reaction.

A density functional theory study on the [3 + 2] cycloaddition of N-(p-methylphenacyl)benzothiazolium ylide and 1-nitro-2-(p-methoxyphenyl) ethene: the formation of two diastereomeric adducts via two different mechanisms

The [3 + 2] cycloaddition reaction of N-(p-methylphenacyl)benzothiazolium ylide (NBY) and 1-nitro-2-(p-methoxyphenyl) ethane (NME), experimentally investigated by Yan et al., was studied theoretically. They reported that the reaction proceeds via a stepwise mechanism and produces two diastereomeric adducts in a 4:1 ratio. For the study of the reaction, two regioselective attacks were considered between the reagents and their theoretical parameters were calculated. In excellent agreement with the experimental outcomes, the Fukui and Parr functions reactivity indices analysis as well as the energetic results indicated that among the two studied regioselective attacks, one which leads to the formation of two experimentally reported adducts, is more favorable than the other. The molecular mechanism of the studied reactions was characterized using the IRC, QTAIM and Wiberg bond indices analyses and the results suggested that two diastereomeric adducts are generated via two different mechanisms. The major adduct is produced via a two-stage one-step mechanism without the formation of any stable intermediate, whereas the minor one is generated through a stepwise mechanism along with the formation of a stable zwitterionic intermediate. The analysis of global electron density transfer showed that the reactions are polar and electron density fluxes from NBY toward NME. It was found from molecular electrostatic potential map that at the more favorable transition state, approach of reactants locates the oppositely charged regions over each other resulting in attractive forces between the two fragments. Analysis of the frontier molecular orbitals indicated that the HOMO orbital of NBY is also a frontier effective-for-reaction molecular orbital.

Revisiting the Modulations of Ionospheric Solar and Lunar Migrating Tides During the 2009 Stratospheric Sudden Warming by Using Global Ionosphere Specification

AbstractIn this study, Global Ionosphere Specification (GIS) based on Gauss‐Markov Kalman filter assimilation of slant total electron content observed from ground‐based global positioning system receivers and space‐based radio occultation instrumentations is applied to investigate the ionospheric day‐to‐day tidal variability during the 2009 stratospheric sudden warming (SSW) period. Including the improved daily three‐dimensional global electron density distribution from GIS enables us to retrieve the daily solar tidal solution by using least squares tidal analysis. We find prominent reductions followed by enhancements in the amplitude of the solar semidiurnal migrating tide (SW2) after the peak warming, with recurrent phase variations occurring at low magnetic latitudes over a period of about 15 days. This is close to the beating period (15.13 day) between SW2 and lunar semidiurnal (M2), thus suggesting the existence of strong M2, and our results demonstrate that the intensification of M2 exists only during the SSW period. Additionally, M2 acts as the key contributor to make the semidiurnal ionospheric perturbations shift toward later local times. Our tidal analyses of daily GIS thus provide evidence for the combined impact of amplitudes and phases of the SW2 and M2 in producing semidiurnal variations in ionosphere during the 2009 SSW.

Theoretical Study of the Possibility of Functionalization of C20 Fullerene with the Simplest Ketene CH2CO

The functionalization is known as a structural modification procedure of fullerenes and carbon nanotubes. This method improves the chemical and physical properties, such as reactivity and solubility. This paper intends to theoretically describe the possibility of functionalization of C20 fullerene with the simplest ketene CH2CO. In the first step, two possible [2+2] and [4+2] cycloaddition reactions between C20 and ketene are considered and simulated theoretically. The results show that the [2+2] reaction is favorable both thermodynamically and kinetically. Also, the IRC analysis of transition states indicates that the reaction takes place via a step-wise mechanism in which a zwitterionic intermediate is generated in a rate-determining step. The solvation effect study based on the CPCM model reveals that by changing the reaction medium from nonpolar to polar, the reaction rate is increased. The NBO analysis and the calculation of global electron density transfer (GEDT) indicate that the reaction involves polar transition states. The calculations of the thermodynamic and kinetic parameters of the [2+2] cycloaddition reaction of bowl C20 with ketene show that this reaction is unfavorable.