Hydrogen and helium escape on Venus via energy transfer from hot oxygen atoms

2020 ◽  
Vol 501 (2) ◽  
pp. 2394-2402
Author(s):  
Hao Gu ◽  
Jun Cui ◽  
Dandan Niu ◽  
Jiang Yu
Keyword(s):  
Cross Sections ◽  
Dominant Role ◽  
Monte Carlo Model ◽  
Dissociative Recombination ◽  
Angle Distribution ◽  
Model Uncertainties ◽  
Atmospheric Escape ◽  
Parallel Approximation ◽  
Hot Oxygen ◽  
Energy Dependent

ABSTRACT Due to the relatively strong gravity on Venus, heavy atmospheric neutrals are difficult to accelerate to the escape velocity. However, a variety of processes, such as the dissociative recombination of ionospheric O$_2^+$, are able to produce hot atoms which could deliver a significant amount of energy to light neutrals and drive their escape. In this study, we construct a Monte Carlo model to simulate atmospheric escape of three light species, H, H2, and He, on Venus via such a knock-on process. Two Venusian background atmosphere models are adopted, appropriate for solar minimum and maximum conditions. Various energy-dependent and species-dependent cross-sections, along with a common strongly forward scattering angle distribution, are used in our calculations. Our model results suggest that knock-on by hot O likely plays the dominant role in driving total atmospheric hydrogen and helium escape on Venus at the present epoch, with a significant portion contributed from regions below the exobase. Substantial variations are also revealed by our calculations. Of special interest is the modelled reduction in escape flux at high solar activities for all species, mainly associated with the enhancement in thermal O concentration near the exobase at high solar activities which hinders escape. Finally, model uncertainties due to several controlling factors, including the distribution of relevant light species in the background atmosphere, the plane-parallel approximation, and the finite O energy distribution, are evaluated.

scholarly journals Monte Carlo calculations of the atmospheric sputtering yields on Titan

2019 ◽  
Vol 623 ◽  
pp. A18 ◽  
Author(s):  
H. Gu ◽  
J. Cui ◽  
D.-D. Niu ◽  
A. Wellbrock ◽  
W.-L. Tseng ◽  
...  
Keyword(s):  
Monte Carlo ◽  
Incidence Angle ◽  
Monte Carlo Model ◽  
High Energy ◽  
Special Focus ◽  
Angle Distribution ◽  
Model Calculations ◽  
Atmospheric Escape ◽  
High Energy Tail ◽  
Sputtering Yields

Context. Sputtering serves as an important mechanism of atmospheric escape in the solar system. Aims. This study is devoted to atmospheric sputtering on Titan, with a special focus on how the N2 and CH4 sputtering yields respond to varying ion incidence energy and angle, and varying ion mass. Methods. A Monte Carlo model was constructed to track the energy degradation of incident ions and atmospheric recoils from which the sputtering yields were obtained. A large number of model runs were performed, taking into account three categories of incident ion with representative masses of 1, 16, and 28 Da, as well as two collision models both characterized by a strongly forward scattering angle distribution, but different in terms of the inclusion or exclusion of electronic excitation of ambient neutrals. Results. Our model calculations reveal substantial increases in both the N2 and CH4 sputtering yields with increasing ion incidence energy and angle, and increasing ion mass. The energy distribution of escaping molecules is described reasonably well by a power law, with an enhanced high energy tail for more energetic incident ions and less massive atmospheric recoils. The CH4-to-N2 sputtering yield ratio is found to range from 10 to 20%, increasing with increasing incidence angle and also increasing with decreasing incidence energy. An approximate treatment of ion impact chemistry is also included in our model, predicting N2 sputtering yields on Titan that are in broad agreement with previous results.

scholarly journals Dayside nitrogen and carbon escape on Titan: the role of exothermic chemistry

2019 ◽  
Vol 633 ◽  
pp. A8 ◽  
Author(s):  
H. Gu ◽  
J. Cui ◽  
P. P. Lavvas ◽  
D.-D. Niu ◽  
X.-S. Wu ◽  
...  
Keyword(s):  
Monte Carlo Model ◽  
Dissociative Recombination ◽  
Escape Rate ◽  
Collisional Quenching ◽  
Escape Probability ◽  
Total N ◽  
Atmospheric Escape ◽  
Climate Evolution ◽  
Rate Profile

Context. Atmospheric escape has an appreciable impact on the long-term climate evolution on terrestrial planets. Exothermic chemistry serves as an important mechanism driving atmospheric escape and the role of such a mechanism is of great interest for Titan due to its extremely complicated atmospheric and ionospheric composition. Aims. This study is devoted to a detailed investigation of neutral N and C escape on the dayside of Titan, which is driven by exothermic neutral–neutral, ion–neutral, and dissociative recombination (DR) reactions. It was carried out based on the extensive measurements of Titan’s upper atmospheric structure by a number of instruments on board Cassini, along with an improved understanding of the chemical network involved. Methods. A total number of 14 C- and N-containing species are investigated based on 146 exothermic chemical reactions that release hot neutrals with nascent energies above their respective local escape energies. For each species and each chemical channel, the hot neutral production rate profile is calculated, which provides an estimate of the corresponding escape rate when combined with the appropriate escape probability profile obtained from a test particle Monte Carlo model. Results. Our calculations suggest a total N escape rate of 9.0 × 1023 s−1 and a total C escape rate of 4.2 × 1023 s−1, driven by exothermic chemistry and appropriate for the dayside of Titan. The former is primarily contributed by neutral-neutral reactions, whereas the latter is dominated by ion–neutral reactions; however, contributions from neutral–neutral and DR reactions to the latter cannot be ignored either. Our calculations further reveal that the bulk of N escape is driven by hot N(4S) production from the collisional quenching of N(2D) by ambient N2, while C escape is mainly driven by hot CH3 and CH4 production via a number of important ion–neutral and neutral–neutral reactions. Conclusions. Considered in the context of prior investigations of other known escape mechanisms, we suggest that exothermic chemistry is likely to contribute appreciably to non-thermal C escape on the dayside of Titan, although it plays an insignificant role in N escape.

SIGMAL: A Program for Calculating L-Shell lonization Cross-Sections

1981 ◽  
Vol 39 ◽  
pp. 198-199 ◽  
Author(s):  
R.F. Egerton
Keyword(s):  
Cross Sections ◽  
Fortran Program ◽  
Absorption Data ◽  
X Ray ◽  
Atomic Electrons ◽  
Energy Dependent ◽  
Hydrogenic Model ◽  
Electron Energy Loss ◽  
X Ray Absorption ◽  
Shell Ionization

SIGMAL is a short (∼ 100-line) Fortran program designed to rapidly compute cross-sections for L-shell ionization, particularly the partial crosssections required in quantitative electron energy-loss microanalysis. The program is based on a hydrogenic model, the L1 and L23 subshells being represented by scaled Coulombic wave functions, which allows the generalized oscillator strength (GOS) to be expressed analytically. In this basic form, the model predicts too large a cross-section at energies near to the ionization edge (see Fig. 1), due mainly to the fact that the screening effect of the atomic electrons is assumed constant over the L-shell region. This can be remedied by applying an energy-dependent correction to the GOS or to the effective nuclear charge, resulting in much closer agreement with experimental X-ray absorption data and with more sophisticated calculations (see Fig. 1 ).

Evaluation of the Pr + O → PrO+ + e− chemi-ionization reaction enthalpy and praseodymium oxide, carbide, dioxide, and carbonyl cation bond energies

2021 ◽  
Vol 23 (4) ◽  
pp. 2938-2952
Author(s):  
Maryam Ghiassee ◽  
Brandon C. Stevenson ◽  
P. B. Armentrout
Keyword(s):  
Cross Sections ◽  
Ion Beam ◽  
Bond Energies ◽  
Reaction Enthalpy ◽  
Praseodymium Oxide ◽  
Guided Ion Beam ◽  
Ionization Reaction ◽  
Lanthanide Metal ◽  
Energy Dependent ◽  
Dependent Product

Guided ion beam tandem mass spectrometry was used to measure the kinetic energy dependent product ion cross sections for reactions of the lanthanide metal praseodymium cation (Pr+) with O2, CO2, and CO and reactions of PrO+ with CO, O2, and Xe.

Dissociative recombination cross sections for NH4+ions and electrons

1978 ◽  
Vol 17 (4) ◽  
pp. 1314-1320 ◽  
Author(s):  
R. D. DuBois ◽  
J. B. Jeffries ◽  
G. H. Dunn
Keyword(s):  
Cross Sections ◽  
Dissociative Recombination

scholarly journals Benchmarking the invariant embedding method against analytical solutions in model transport problems

2006 ◽  
Vol 21 (2) ◽  
pp. 3-13
Author(s):  
Malin Wahlberg ◽  
Imre Pázsit
Keyword(s):  
Half Space ◽  
Cross Sections ◽  
Length Distribution ◽  
Infinite Medium ◽  
Scattering Medium ◽  
Embedding Method ◽  
Invariant Embedding ◽  
Invariant Embedding Method ◽  
Transport Problems ◽  
Energy Dependent

The purpose of this paper is to demonstrate the use of the invariant embedding method in a few model transport problems for which it is also possible to obtain an analytical solution. The use of the method is demonstrated in three different areas. The first is the calculation of the energy spectrum of sputtered particles from a scattering medium without absorption, where the multiplication (particle cascade) is generated by recoil production. Both constant and energy dependent cross-sections with a power law dependence were treated. The second application concerns the calculation of the path length distribution of reflected particles from a medium without multiplication. This is a relatively novel application, since the embedding equations do not resolve the depth variable. The third application concerns the demonstration that solutions in an infinite medium and in a half-space are interrelated through embedding-like integral equations, by the solution of which the flux reflected from a half-space can be reconstructed from solutions in an infinite medium or vice versa. In all cases, the invariant embedding method proved to be robust, fast, and monotonically converging to the exact solutions.

scholarly journals Impact of cirrus clouds heterogeneities on top-of-atmosphere thermal infrared radiation

2014 ◽  
Vol 14 (11) ◽  
pp. 5599-5615 ◽  
Author(s):  
T. Fauchez ◽  
C. Cornet ◽  
F Szczap ◽  
P. Dubuisson ◽  
T. Rosambert
Keyword(s):  
Radiative Transfer ◽  
Monte Carlo Model ◽  
Thermal Infrared ◽  
Brightness Temperatures ◽  
Spectral Bands ◽  
Thickness Standard ◽  
The Difference ◽  
Scale Properties ◽  
Parallel Approximation ◽  
The Impact

Abstract. This paper presents a study of the impact of cirrus cloud heterogeneities on the thermal infrared brightness temperatures at the top of the atmosphere (TOA). Realistic 3-D cirri are generated by a cloud generator based on simplified thermodynamic and dynamic equations and on the control of invariant scale properties. The 3-D thermal infrared radiative transfer is simulated with a Monte Carlo model for three typical spectral bands in the infrared atmospheric window. Comparisons of TOA brightness temperatures resulting from 1-D and 3-D radiative transfer show significant differences for optically thick cirrus (τ > 0.3 at 532 nm) and are mainly due to the plane-parallel approximation (PPA). At the spatial resolution of 1 km × 1 km, two principal parameters control the heterogeneity effects on brightness temperatures: i) the optical thickness standard deviation inside the observation pixel, ii) the brightness temperature contrast between the top of the cirrus~and the clear-sky atmosphere. Furthermore, we show that the difference between 1-D and 3-D brightness temperatures increases with the zenith view angle from two to ten times between 0° and 60° due to the tilted independent pixel approximation (TIPA).

Target electron removal in C5+ + H collision

2021 ◽  
Author(s):  
Saed J Al Atawneh ◽  
Karoly Tokesi
Keyword(s):  
Monte Carlo ◽  
Cross Sections ◽  
Dominant Role ◽  
Correction Term ◽  
Theoretical Data ◽  
Model Potential ◽  
Classical Trajectory ◽  
Projectile Energy ◽  
Collision Dynamics ◽  
The Cross

Abstract We present target ionization and charge exchange cross sections in a collision between C5+ ion and H atom. We treat the collision dynamics classically using a four-body classical trajectory Monte Carlo (CTMC) and a four-body quasi-classical Monte Carlo (QCTMC) model when the Heisenberg correction term is added to the standard CTMC model via model potential. The calculations were performed in the projectile energy range between 1.0 keV/amu and 10 MeV/amu. We found that the cross sections obtained by the QCTMC model are higher than that of the cross sections calculated by the standard CTMC model and these cross sections are closer to the previous experimental and theoretical data. Moreover, for the case of ionization, we show that the interaction between the projectile and the target electrons plays a dominant role in the enhancement of the cross sections at lower energies.

scholarly journals Charge Exchange Cross Sections for Noble Gas Ions and N2 between 0.2 and 5.0 keV

Atoms ◽  
2019 ◽  
Vol 7 (4) ◽  
pp. 96
Author(s):  
Steven Bromley ◽  
Corey Ahl ◽  
Chad Sosolik ◽  
Joan Marler
Keyword(s):  
Charge Exchange ◽  
Cross Sections ◽  
Neutral Atom ◽  
Mechanical Design ◽  
Noble Gas ◽  
Dominant Role ◽  
Intermediate Energy ◽  
Fundamental Interaction ◽  
Gas Cell ◽  
Astrophysical Plasmas

Charge transfer of an electron from a neutral atom to an ion is a fundamental interaction that plays a dominant role in the energy balance of atmospheric and astrophysical plasmas. The present investigation measured the charge exchange cross sections of noble gas ions (He + , Ne + , Ar + , Kr + ) with N 2 in the intermediate energy range 0.2–5.0 keV. The systems were chosen because there remains a lack of consensus amongst previous measurements and regions where there were no previous measurements. A description of the mechanical design for an electrically floated gas cell is described herein.

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