Monthly Notices is one of the three largest general primary astronomical research publications. It is an international journal, published by the Royal Astronomical Society. This article 1 describes its publication policy and practice.

Monthly Notices of the Royal Astronomical Society

/pdf/fundamentals-and-applications-of-atmospheric-pressure-3h6qqusyxt.pdf

Fundamentals and Applications of Atmospheric Pressure Plasmas

We study the process of laser-assisted dissociative recombination of an electron with a molecular cation using a semiclassical approach. In the region outside a reaction sphere the electron motion in the combined laser and Coulomb fields is treated classically. Within the sphere the laser-field effects are neglected, and the recombination probability is obtained from quantum-mechanical cross sections calculated for the laser-free process. Specific calculations are performed for dissociative recombination of ${\mathrm{H}}_{2}^{+}$ in the field of the intensity 2.09 GW/${\mathrm{cm}}^{2}$ and the wavelength $22.8\phantom{\rule{4pt}{0ex}}\ensuremath{\mu}\mathrm{m}$. In the energy region above 1 meV the cross section is significantly enhanced compared with the field-free case due to the Coulomb focusing effect. The influence of the indirect process due to electron capture into Rydberg states is also investigated. Although the Rydberg resonances are washed out due to the field effects, they influence significantly the magnitude of the dissociative recombination cross section.

Semiclassical theory of laser-assisted dissociative recombination

The first comprehensive study of electron gains and losses in hypersonic air flows including the full coupling between the non-neutral plasma sheaths and the quasi-neutral plasma flow is here presented. Such is made possible by the use of advanced numerical methods that overcome the stiffness associated with the plasma sheaths. The coupling between the sheaths, the electron temperature in non-equilibrium, and the ambipolar diffusion within the quasi-neutral plasma flow is found to be critical to predict accurately electron losses and, thus, plasma density around hypersonic vehicles. This is because electron cooling coming from the non-neutral sheaths affects significantly electron temperature everywhere in the plasma and, therefore, the electron-temperature-dependent loss processes of ambipolar diffusion and dissociative recombination. Results obtained show that electron loss to the surface due to catalyticity dominates over electron loss within the plasma due to dissociative recombination either (i) at high altitude where the dynamic pressure is low, or (ii) at low Mach number, or (iii) when the vehicle has a sharp leading edge. 

/pdf/electron-losses-in-hypersonic-flows-1oi1w036.pdf

Electron losses in hypersonic flows

The Rayleigh-Debye-Gans approximation for fractal aggregates (RDG-FA) is commonly used to evaluate the radiative properties of soot aerosols composed of nano-spheres due to its analytical character. Despite neglecting electromagnetic coupling within an aggregate, the RDG-FA provides a simple interpretation of angular light-scattering measurements in terms of a structure factor. This factor, in turn, enables the determination of the aggregate’s fractal dimension Df and radius of gyration Rg. The structure factor can be expressed as the Fourier transform of a purely morphological autocorrelation function. Here we employ the discrete dipole approximation and phasor analysis of the internal electric field in an aggregate to study the role of coupling for the specific case of soot particle refractive index. An optical autocorrelation function is defined in terms of an aggregate’s phasors rather than simply its physical distribution of material. The new function conveys the effect of the non-uniformity of the internal field distribution, due to coupling, to the angular scattering. A correction term is then introduced explaining why coupling tends to decrease the structure factor inferred in the power-law regime. Such decrease impacts the determination of the fractal dimension from scattering data. Finally, it is shown that the inferred structure factor is mainly affected by a so-called internal trapping effect associated with a large imaginary part of the refractive index. 

Electromagnetic coupling and determination of the structure factor of fractal aggregates

Cross sections and thermal rate coefficients are computed for electron-impact dissociative recombination and vibrational excitation/de-excitation of the N 2 + molecular ion in its lowest six vibrational levels, for collision energies/temperatures up to 2.3 eV/5000 K.

/pdf/low-energy-electron-impact-dissociative-recombination-and-20k0j0vhw7.pdf

Low-energy electron impact dissociative recombination and vibrational transitions of N 2 +

• The internal electric field of fractal aggregates is studied with a phasor approach. • Internal coupling and absorption explain the RDG-FA discrepancies for large aggregates. • Aggregate size, monomer radius, refractive index, and wavelength dependencies are investigated. • Semi-empirical corrections for the RDG-FA derived forward-scattering and absorption are proposed. The Rayleigh Debye-Gans approximation for Fractal Aggregates (RDG-FA) is commonly used for the evaluation of the radiative properties of fractal aggregates of nanometer-scale nearly spherical particles as soot particles. The cost of its simplicity, however, is the precision of the aggregate cross sections when the refractive index deviates from unity and when the aggregate’s spheres, or monomers, are not sufficiently small compared to the wavelength. While correction factors have been highlighted before, their physical origin is not clear and no universal correction factors are proposed. The present study develops an approach based on phasor analysis of the aggregate’s internal electric field rigorously determined by the discrete dipole approximation. Aggregates representative of the Diffusion Limited Cluster Aggregation (DLCA) regime having a fractal dimension of D f = 1.78 are considered as representative of a soot aggregate. The results reveal that correction factors to the RDG-FA for forward scattering ( A ) and the absorption cross section ( h ) are due to a competition between internal-field hot-spots caused by point contact between the spherical monomers and a decrease of the field amplitude as the field propagates through the aggregate. Both phenomena are neglected in the RDF-FA by definition. The absorption phenomenon explains the aggregate-size dependence of A and h . These effects are then studied as the aggregate size varies according to the number of monomers N m ranging from 10 to 1000, as the monomer radius varies from R m = 5 nm - 30 nm , and as the wavelength varies from λ = 266 nm - 1064 nm . Both constant and wavelength dependent refractive indices for organic, graphitic, and amorphous soot are considered. Finally, a semi-empirical model is proposed intended to correct the RDG-FA theory based on the analysis. 

http://manuscript.elsevier.com/S0022407322000802/pdf/S0022407322000802.pdf

C. Argentin

Papers

Low-energy electron impact dissociative recombination and vibrational transitions of N 2 +

A semi-empirical correction for the Rayleigh-Debye-Gans approximation for fractal aggregates based on phasor analysis: Application to soot particles

Electromagnetic coupling and determination of the structure factor of fractal aggregates

Electron dissociative attachement to ArH + , HD + , N 2 + and CO 2