Excitation of Electronic States of CO in Radio-Frequency Electric Field by Electron Impact

Electron impact excitation rate coefficients for singlet and triplet electronic states of the carbon monoxide molecule have been calculated under non-equilibrium conditions in the presence of radio-frequency electric field. A Monte Carlo simulation of electron transport has been performed in order to determine non-equilibrium electron energy distribution functions within one period of applied electric field. By using these distribution functions and corresponding cross sections, the excitation rate coefficients have been calculated for all electronic states of CO in the frequency range from 13.56 up to 500 MHz, at reduced root mean square electric field values ranging from 200 to 700 Td. We expect these rates to be valuable for modeling radio-frequency CO plasmas since excited neutrals exhibit greater chemical reactivity than neutrals in ground electronic state, hence altering many properties of plasma.     

Rate coefficients for resonant vibrational excitation of CO

Rate coefficients for vibrational excitation of the carbon-monoxide molecule, via the ²Π shape resonance in the energy region from 0 eV to 5 eV have been calculated. Calculations are performed for a Maxwellian electron energy distribution by using our recent experimentally measured differential cross sections for excitation of the first 10 vibrational levels. By using extended Monte Carlo simulations the electron energy distribution functions (EEDFs) and rate coefficients are determined in non-equilibrium conditions, in the presence of a homogeneous electric field. Calculations are performed for typical, moderate values of the electric field over gas number density ratios, E/N. A difference between Maxwellian and non-equilibrium rate coefficients was found due to a specific shape of the electron energy distribution function under the considered conditions.     

Resonant vibrational excitation and de-excitation of N2(v) by low-energy electrons

We have calculated cross sections and rate coefficients for low-energy electron impact excitation of the nitrogen molecule from vibrationally excited levels N2(v) 1-8. Calculations are performed in the 2Pig shape resonance energy region, from 0 to 5 eV. The cross sections are determined by using our recent integral cross section measurements of the ground level vibrational excitation and the most recent cross sections for elastic electron scattering, applying the principle of detailed balance. The rate coefficient calculations are performed for the Maxwellian electron energy distribution. By using extended Monte Carlo simulations, the electron energy distribution functions (EEDF) and the rate coefficients are also determined for the nonequilibrium conditions, in the presence of the homogeneous external electric field for the typical, moderate values of the electric field over gas number density ratios, E/N.     

BN Nanotube Serving as a Gas Chemical Sensor for N<Subscript>2</Subscript>O by Parallel Electric Field

Density functional theory calculations were performed to understand the electronic properties of C₂₄, B₁₂N₁₂, B₁₂P₁₂, and (6, 0) BNNT interacted with N₂O molecule in the presence and absence of an external electric field using the B3LYP method and 6-31G** basis set. The adsorption of N₂O from O-side on the surface of (6, 0) BNNT has high sensitivity in comparison with B₁₂N₁₂ nano-cage. The adsorption energy of N₂O (O-side) on the sidewalls of B₁₂N₁₂ and BNNT in the presence of an electric field are ?21.01 and ?15.48 kJ mol^?1, respectively. Our results suggest that in the presence of an electric field, the B₁₂N₁₂ nano-cage is the more energetically notable upon the N₂O adsorption than (6, 0) BNNT, C₂₄, and B₁₂P₁₂. Whereas, our results indicate that the electronic property of BNNT is more sensitive to N₂O molecule at the presence of an electric field than B₁₂N₁₂ nano-cage. It is anticipated that BNNT could be a favorable gas sensor for the detection of N₂O molecule.     

Ionization and Electronic State Excitation of CO2 in Radio-frequency Electric Field

Plasma Chemistry and Plasma Processing - The rate coefficients for the electron impact ionization and electronic state excitation of the CO2 molecule are calculated in non-equilibrium conditions in...     

Resonant vibrational excitation and de-excitation of CO(v) by low energy electrons

Integral cross sections and rate coefficients for vibrational excitation of the excited carbon-monoxide molecule, via the (2)Pi shape resonance in the energy region from 0 to 5 eV have been calculated. Cross sections are calculated by using our recently measured cross sections for the ground level CO excitation and the most recent cross sections for elastic electron scattering, applying the principle of detailed balance. Rate coefficients are calculated for Maxwellian electron energy distribution, with mean electron energies below 5 eV. By using extended Monte Carlo simulations, electron energy distribution functions (EEDF) and rate coefficients are determined in nonequilibrium conditions, in the presence of homogeneous external electric field. Nonequilibrium rates are calculated for typical, moderate values of the electric field over gas number density ratios, E/N, from 1 to 220 Td. Maxwellian and nonequilibrium rate coefficients are compared and the difference is attributed to a specific shape of the electron energy distribution functions under considered conditions.     

Generation of Antimicrobial NO<Subscript>x</Subscript> by Atmospheric Air Transient Spark Discharge

Atmospheric pressure air plasma discharges generate potential antimicrobial agents, such as nitrogen oxides and ozone. Generation of nitrogen oxides was studied in a DC-driven self-pulsing (1–10 kHz) transient spark (TS) discharge. The precursors of NO_x production and the TS characteristics were studied by nanosecond time-resolved optical diagnostics: a photomultiplier module and a spectrometer coupled with fast intensified camera. Thanks to the short (~10–100 ns) high current (>1 A) spark current pulses, highly reactive non-equilibrium plasma is generated. Ozone was not detectable in the TS, probably due to higher gas temperature after the short spark current pulses, but the NO_x production rate of ~7 × 10¹⁶ molecules/J was achieved. The NO₂/NO ratio decreased with increasing TS repetition frequency, which is related to the complex frequency-dependent discharge properties and thus changing NO₂/NO generating mechanisms. Further optimization of NO₂ and NO production to improve the biomedical and antimicrobial effects is possible by modifying the electric circuit generating the TS discharge.     

A DFT study on electronic and optical properties of aspirin-functionalized B<Subscript>12</Subscript>N<Subscript>12</Subscript> fullerene-like nanocluster

In this work, the interaction of an aspirin (AS) molecule with the external surface of a boron nitride fullerene-like nanocage (B₁₂N₁₂) is studied by means of density functional theory (DFT) calculations. Equilibrium geometry, electronic properties, adsorption energy and thermodynamic stability are identified for all of the adsorbed configurations. Four stable configurations are obtained for the interaction of AS molecule with the B₁₂N₁₂ nanocage, with adsorption energies in the range of ?10.1 to ?37.7 kcal/mol (at the M06-2X/6-31 + G** level). Our results clearly indicate that Al-doping of the B₁₂N₁₂ tends to increase the adsorption energy and thermodynamic stability of AS molecule over this nanocage. We further study the adsorption of AS over the B₁₂N₁₂ and B₁₁N₁₂Al in the presence of a protic (water) or aprotic (benzene) solvent. It is found that the calculated binding distances and adsorption energies by the PCM and CPCM solvent models are very similar, especially for the B₁₂N₁₂ complexes. According to time-dependent DFT calculations, the Al-doping can shift estimated λ _max values toward longer wavelengths (redshift). Solvent effects also have an important influence on the calculated electronic absorption spectra of AS-B₁₂N₁₂ complexes.     

Combined Diffusion Coefficients in CO<Subscript>2</Subscript> Thermal Plasmas Contaminated with Cu,Fe or Al

Our work aims at the computation of combined diffusion coefficients in CO₂–metal (Cu, Fe, Al) mixtures at a temperature interval of 2000–30,000 K at 0.1 MPa and aims at the investigation of the impact of the concentration and nature of metal vapor (Cu, Fe, Al) on diffusion phenomena. The combined diffusion coefficients have four components, more specifically, combined ordinary diffusion coefficient, combined electric field diffusion coefficient, combined temperature diffusion coefficient and combined pressure diffusion coefficient due to the gradients of the species densities, applied electrical field temperature and pressure. The results indicate that, for Cu and Fe, the combined diffusion coefficients are quite identical under the condition of same metal concentrations (1 and 10% mass concentration). Compared with Cu and Fe under the same metal concentrations (1 and 10%), Al results in a larger enhancement of combined electric field and ordinary diffusion coefficients while smaller enhancement of combined temperature diffusion coefficients. All the combined diffusion coefficients exhibit an upward trend with metal concentrations except for combined electric field, temperature and pressure diffusion coefficients. These three mentioned coefficients are attenuated by the metal vapor above the certain concentration such as, in the case of combined temperature diffusion coefficients, 70% Cu, 70% Fe and 50% Al for CO₂–Cu, CO₂–Fe and CO₂–Al mixtures respectively. Namely, compared with Cu and Fe, less quantity of Al is required to achieve the maximum of combined diffusion coefficients. Maximum peaks for the combined coefficients are shifted to the higher temperature with increasing metal concentrations.     

Finite-field many-body perturbation theory. X. Electric field gradients and other properties of N2

Finite-field MBPT calculations have been carried out for the electric field gradient and other electric properties of the nitrogen molecule. On the basis of correlation corrections computed through the fourth order in the electron correlation perturbation the infinite order MBPT result for the electric field gradient at the nitrogen nucleus has been estimated. The corresponding result combined with the NQR coupling constant for N₂ leads to the ¹⁴N nuclear quadrupole moment of 0.0205 ± 0.0010 barn in agreement with the experimental atomic measurement and other molecular calculations. The MBPT estimate of the quadrupole moment of N₂ gives −1.107 ± 0.038 au in agreement with the most recent experimental value.     

Combined Application of Optical Emission Spectroscopy and Kinetic Numerical Modelling to Determine the Ions Densities in a Flowing N<Subscript>2</Subscript> Post-Discharge

The combined application of optical emission spectroscopy (OES) and kinetic numerical modelling was employed to determine the N₂⁺(X²\( \Sigma_{\text{g}}^{ + } \)), N₃⁺, and N₄⁺ densities in the post-discharge (pink afterglow; PA) of a nitrogen flowing DC discharge. We measured the relative densities of the N₂(C³Π_u) and N₂⁺(B²\( \Sigma_{\text{u}}^{ + } \)) states along the post-discharge region by OES. The density values were attained as functions of the post-discharge residence time. We fitted the experimental densities with densities calculated from a kinetic numerical model developed to calculate the temporal density of several nitrogen species in the nitrogen afterglow. Analysis of the rate balance equations of these ions indicated that these densities can be determined from data generated from both the model and experimental N₂⁺(B²\( \Sigma_{\text{u}}^{ + } \)) density. Thus, we determined the ions density profiles in the nitrogen post-discharge and observed that the N₃⁺ density is dominant in the PA. This is followed by that of the N₂⁺(X²\( \Sigma_{\text{g}}^{ + } \)) and N₄⁺ ions. Such behaviour has been previously reported in a study that employed mass spectrometry to analyse the ions in the PA generated by a nitrogen high-frequency discharge. In our study, the DC discharge was operated at a gas flow rate of 0.9 Slm^?1, a discharge current of 30 mA, and a gas pressure range of 400–700 Pa.     

Electron energy distribution functions and rate and transport coefficients of H2/H/CH4 reactive plasmas for diamond film deposition

Electron energy distribution functions (eedf) and rate and transport coefficients for H₂/H/CH₄ mixtures have been calculated by solving a stationary Boltzmann equation as a function of reduced electric field E/N, of molar fraction, and of different concentrations of electronically excited states. Superelastic electronic collisions superimpose structures to eedf especially for E/N values < 40 Td.     

Cross sections and rate coefficients for electronic excitation of the triplet states of the hydrogen molecule in different vibrational levels

Cross sections for the excitation of the triplet state of H₂ from different vibrational levels of the ground electronic state have been calculated by using the Gryzinski approximation. The results for the ground vibrational level are in satisfactory agreement with the corresponding values obtained by the quantum mechanical close coupling method. The calculated cross sections have been used to generate rate coefficients for the excitation of the triplet states by using a self-consistent electron energy distribution function, obtained by numerical integration of the Boltzmann equation. The results show a strong increase of the different rate coefficients with increasing the vibrational quantum number.     

Investigation of the S<Subscript>0</Subscript>S<Subscript>1</Subscript> excitation in bacteriorhodopsin with the ONIOM(MO:MM) hybrid method

 We have investigated the S₀ and S₁ electronic states in bacteriorhodopsin using a variety of QM/MM levels. The decomposition of the calculated excitation energies into electronic and electrostatic components shows that the interaction of the chromophore with the protein electric field increases the excitation energy, while polarization effects are negligible. Therefore, the experimentally observed reduction in excitation energy from solution phase to protein environment (the Opsin shift) does not come from the electrostatic interaction with the protein environment, but from either the interaction ofthe chromophore with the solvent or counter ion, or structural effects. Our high-level ONIOM(TD– B3LYP:Amber) calculation predicts the excitation energy within 8 kcal/mol from experiment, the discrepancy probably being caused by the neglect of polarization of the protein environment. In addition, we have shown that the level of optimization is extremely critical for the calculation of accurate excitation energies in bacteriorhodopsin. Received: 13 October 2001 / Accepted: 6 September 2002 / Published online: 3 February 2003 Contribution to the Proceedings of the Symposium on Combined QM/MM Methods at the 222nd National Meeting of the American Chemical Society, 2001 Correspondence to: K. Morokuma e-mail: morokuma@emory.edu     

The Role of Y<Subscript>2</Subscript>O<Subscript>3</Subscript> and MgO Additives on the Photoluminescence Properties of Si<Subscript>3</Subscript>N<Subscript>4</Subscript> Nanoparticles

The current research addressed synthesizing and studying photoluminescence studies of β-Si₃N₄ nanoparticles. The effect of MgO and Y₂O₃ as the typical additives on photoluminescence behaviour was evaluated. The β-Si₃N₄ with MgO and Y₂O₃ additive specimens were fabricated by a solid state technique (ball-milled method). The as-prepared products were characterized by X-ray diffraction technique, transmission electron microscopy, field emission scanning electron microscopy, energy dispersive X-ray spectroscopy and Raman analysis. The results showed that after ball-milled process, hexagonal β-Si₃N₄ with MgO or Y₂O₃ as the additives with the size distribution of 45–50 nm was obtained. The optical properties of the as-synthesized product were also investigated by photoluminescence and diffuse reflection spectroscopy. The obtained results confirmed that employing MgO as an additive, in comparison to the Y₂O₃, could enhance emission properties in the synthesized silicon nitride nanoparticles. The obtained results also showed that MgO–Si₃N₄ pair acted as FRET system to enhance the emission intensity of β-Si₃N₄ nanoparticles.     

Preparation and characterization of H<Subscript>3</Subscript>PW<Subscript>12</Subscript>O<Subscript>40</Subscript>/ZrO<Subscript>2</Subscript> catalyst for carbonation of methanol into dimethyl carbonate

A H₃PW₁₂O₄₀/ZrO₂ catalyst for effective dimethyl carbonate (DMC) formation via methanol carbonation was prepared using the sol–gel method. X-ray photoelectron spectra showed that reactive and dominant (63%) W(VI) species, in WO₃ or H₂WO₄, enhanced the catalytic performances of the supported ZrO₂. The mesoporous structure of H₃PW₁₂O₄₀/ZrO₂ was identified by nitrogen adsorption–desorption isotherms. In particular, partial sintering of catalyst particles in the duration of methanol carbonation caused a decrease in the Brunauer–Emmett–Teller surface area of the catalyst from 39 to 19 m²/g. The strong acidity of H₃PW₁₂O₄₀/ZrO₂ was confirmed by the desorption peak observed at 415 °C in NH₃ temperature-programmed desorption curve. At various reaction temperatures (T?=?110, 170, and 220 °C) and CO₂/N₂ volumetric flow rate ratios (CO₂/N₂?=?1/4, 1/7, and 1/9), the calculated catalytic performances showed that the optimal methanol conversion, DMC selectivity, and DMC yield were 4.45, 89.93, and 4.00%, respectively, when T?=?170 °C and CO₂/N₂?=?1/7. Furthermore, linear regression of the pseudo-first-order model and Arrhenius equation deduced the optimal rate constant (4.24?×?10^?3 min^?1) and activation energy (E_a?=?15.54 kJ/mol) at 170 °C with CO₂/N₂?=?1/7 which were favorable for DMC formation.     

Synthesis and charge-discharge performance of Li<Subscript>5</Subscript>SiN<Subscript>3</Subscript> as a cathode material of lithium secondary batteries

Li₅SiN₃ crystals are synthesized by direct reaction between Li₃N and Si₃N₄ with the molar ratio Li₃N/Si₃N₄ of 10:1. Reaction is performed at 1073 K for 1 h under a nitrogen atmosphere of 700 Torr. The lattice constant determined by the X-ray powder diffraction method is 4.718 Å. Four broad Raman peaks are observed at 196, 286, 580, and 750 cm^?1. By analogy with LiMgN, the broad peak at 580 cm^?1 with a half width of 140 cm^?1 is attributed to homogenously random distribution of Li and Si atoms. The band gap of Li₅SiN₃ is found to be a direct gap of about 2.5 eV by optical absorption and photoacoustic spectroscopy methods. Comparison with the conventional cathode materials for lithium ion batteries, this gap value is close to d-d transition energy of Mn in LiMn₂O₄ (1.63 eV or 2.00 eV) and that of Co in LiCoO₂ (2.1 eV), suggesting that Li₅SiN₃ is a possible cathode material. The 5 × 5 mm²-sized lithium secondary battery of Li₅SiN₃ cathode/propylene carbonate + LiClO₄ electrolyte/Li anode structure shows a discharge capacity of 2.4 μAh cm^?2 for a discharge current of 1.0 μA.     

An octahedral nickel(II) complex of a hexadentate N<Subscript>2</Subscript>O<Subscript>2</Subscript>S<Subscript>2</Subscript> thioether ligand: synthesis,characterization, X-ray and electronic structure

A hexadentate dibasic thioether N₂O₂S₂ donor ligand (H ₂ L) and its octahedral nickel(II) complex, [Ni(L)] have been synthesized and characterized by physicochemical and spectroscopic techniques. The structures of both H ₂ L and its nickel complex were confirmed by single-crystal X-ray diffraction studies. The cyclic voltammogram of the complex shows a quasi-reversible Ni(II)/Ni(III) oxidation couple (E _1/2 = 0.88 V) along with a ligand-based reduction (E _1/2 = ?0.83 V). The electronic structures and electrochemical properties have been interpreted with the help of DFT calculations. The electronic transitions as calculated by TDDFT/CPCM method are used to assign the UV–Vis absorption bands.     

State-to-state dissociation rate coefficients in electronically excited diatomic gases

In the present Letter, state dependent dissociation rate coefficients in diatomic gases with non-equilibrium vibrational and electronic excitation and chemical reactions are studied. A widely used Treanor–Marrone model is generalized to take into account state-to-state vibrational and electronic distributions. The influence of electronic excitation on the rate of dissociation from various electronic states of CO molecules is estimated.     

Multi-Component Diffusion Coefficients in Nitrogen Plasma Under Thermal Equilibrium and Non-equilibrium Conditions

Multi-component diffusion coefficients are calculated for a seven species model of nitrogen plasma under thermal non-equilibrium following the first order perturbation technique of Chapman and Enskog. Binary, thermal, thermal ambipolar, general and general ambipolar diffusion coefficients are presented over electron temperatures ranging from 300 to 50,000 K and thermal non-equilibrium parameter (Te/Th) ranging from 1 to 5. Considering large volume of data, binary, general and general ambipolar diffusion coefficients are presented only for atmospheric pressure. Thermal and thermal ambipolar diffusion coefficients are presented for pressures ranging from 0.1 to 2 atm. The results are compared with published experimental and theoretical data. Necessary electronic levels, associated transition data and collision integrals are collected from recent literature. Details of behaviour of each of the coefficients are presented.