Positive ion reactions

1969 ◽  
Vol 47 (10) ◽  
pp. 1797-1807 ◽  
Author(s):  
Wade L. Fite
Keyword(s):  
Cross Sections ◽  
Rate Coefficients ◽  
The Past ◽  
Positive Ions ◽  
The Earth ◽  
Positive Ion

Progress over the past five years in the measurement of rate coefficients and cross sections for interactions between positive ions and neutral molecules of particular interest to aeronomy is reviewed. Emphasis is placed on the methods of experimentation developed for studies in the range of thermal energies and slightly above. Along with discussion of the range of applicability of each of the techniques, illustrated by examples of measurements on processes of aeronomic interest, some evaluation of limitations of applicability and reliability of the measurements is made. A table summarizing results obtained to date on processes pertaining to the atmospheres of the earth and neighboring planets is presented.

scholarly journals A new process of negative-ion formation. IV

1938 ◽  
Vol 168 (932) ◽  
pp. 103-122 ◽  
Keyword(s):  
Negative Ions ◽  
Senior Author ◽  
Negative Ion ◽  
The Past ◽  
Ion Formation ◽  
Positive Ions ◽  
New Process ◽  
The Difference ◽  
To Come ◽  
Positive Ion

The three previous papers of this series (Arnot and Milligan 1936 b ; Arnot 1937 a, b ) contain an account of experimental work which led the senior author to propose a new process of negative-ion formation. This process is the formation of negative ions at metal surfaces by bombardment of the surface with positive ions, the negative ion being formed by the positive ion capturing two electron from the surface. Further work carried out during the past year, which is described in this paper, has revealed a new variation of the above process. In this latter process the impinging positive ion causes an adsorbed atom on the surface to come off as a negative ion. It is believed that this newer process is essentially similar to the process previously reported, the difference being due merely to the transference of excitation energy from the incident positive ion, after its capture of an electron, to the atom adsorbed on the surface. The discovery of this second effect was made independently by Sloane and Press (1938), although they attribute it to a different process.

Using the effective recombination coefficient to constrain the positive ion composition in Saturn's ionosphere

2020 ◽  
Author(s):  
Joshua Dreyer ◽  
Erik Vigren ◽  
Michiko Morooka ◽  
Jan-Erik Wahlund ◽  
Stephan Buchert ◽  
...  
Keyword(s):  
Electron Temperature ◽  
Recombination Rate ◽  
Lower Ionosphere ◽  
Negative Ions ◽  
Rate Coefficients ◽  
Recombination Coefficient ◽  
Positive Ions ◽  
Electron Production ◽  
Upper Limits ◽  
Positive Ion

<p>We combine RPWS/LP and INMS data from Cassini's Grand Finale orbits into Saturn's lower ionosphere to calculate the effective recombination coefficient α<sub>300</sub> at a reference electron temperature of 300 K. Assuming photochemical equilibrium at altitudes below 2500 km and using an established method to determine the electron production rate, we derive upper limits for α<sub>300</sub> of ∼ 2.5∗10<sup>-7</sup> cm<sup>3 </sup>s<sup>-1</sup>, which suggest that Saturn's ionospheric positive ions are dominated by species with low recombination rate coefficients.<br />An ionosphere dominated by water group ions or complex hydrocarbons, as previously suggested, is incompatible with this result, as these species have recombination rate coefficients > 5∗10<sup>-7</sup> cm<sup>3 </sup>s<sup>-1</sup> at an electron temperature of 300 K. The results do not give constraints on the nature of the negative ions.</p>

scholarly journals Secondary Electron Emission from Solid Surfaces Bombarded by Medium Energy Ions

1971 ◽  
Vol 24 (4) ◽  
pp. 859 ◽  
Author(s):  
ER Cawthron
Keyword(s):  
Cross Sections ◽  
Secondary Electron Emission ◽  
Statistical Treatment ◽  
Solid Surfaces ◽  
Ionization Cross ◽  
Positive Ions ◽  
Interaction Processes ◽  
Reasonable Range ◽  
Ionization Cross Sections ◽  
Positive Ion

The results of Cawthron, Cotterell, and Oliphant for the emission of electrons produced by bombardment of a metal surface with various kinds of positive ions are compared with the predictions of proposed theories. It is seen that the complexity of the interaction processes occurring when a positive ion enters a surface is such that the emission process can only be described in a non-analytical manner, using a statistical treatment. The following discussion indicates that the observed results can be predicted qualitatively over a reasonable range of bombarding energies for many targets and ions by applying the theory of Parilis and Kishinevski. The energy loss cross sections, as well as the actual ionization cross sections, are shown to be important factors in determining the total emission.

The Origin of the Moon and its Relationship to the Origin of the Solar System

1962 ◽  
Vol 14 ◽  
pp. 133-148 ◽  
Author(s):  
Harold C. Urey
Keyword(s):  
Solar System ◽  
The Moon ◽  
The Past ◽  
The Earth ◽  
Short Period ◽  
Origin Of The Moon

During the last 10 years, the writer has presented evidence indicating that the Moon was captured by the Earth and that the large collisions with its surface occurred within a surprisingly short period of time. These observations have been a continuous preoccupation during the past years and some explanation that seemed physically possible and reasonably probable has been sought.

A New AID for Interpolating and Assessing Collision Strengths and Rate Coefficients

1988 ◽  
Vol 102 ◽  
pp. 107-110
Author(s):  
A. Burgess ◽  
H.E. Mason ◽  
J.A. Tully
Keyword(s):  
Significant Loss ◽  
Impact Excitation ◽  
Rate Coefficients ◽  
Electron Impact Excitation ◽  
Graphical Display ◽  
Practical Procedure ◽  
Positive Ions ◽  
Allowed Transition ◽  
Computational Errors ◽  
Existing Data

AbstractA new way of critically assessing and compacting data for electron impact excitation of positive ions is proposed. This method allows one (i) to detect possible printing and computational errors in the published tables, (ii) to interpolate and extrapolate the existing data as a function of energy or temperature, and (iii) to simplify considerably the storage and transfer of data without significant loss of information. Theoretical or experimental collision strengths Ω(E) are scaled and then plotted as functions of the colliding electron energy, the entire range of which is conveniently mapped onto the interval (0,1). For a given transition the scaled Ω can be accurately represented - usually to within a fraction of a percent - by a 5 point least squares spline. Further details are given in (2). Similar techniques enable thermally averaged collision strengths upsilon (T) to be obtained at arbitrary temperatures in the interval 0 < T < ∞. Application of the method is possible by means of an interactive program with graphical display (2). To illustrate this practical procedure we use the program to treat Ω for the optically allowed transition 2s → 2p in ArXVI.

Rotational de-excitations of C3H+ (1Σ+) by collision with He: new ab initio potential energy surface and scattering calculations

2020 ◽  
Vol 494 (4) ◽  
pp. 5675-5681 ◽  
Author(s):  
Sanchit Chhabra ◽  
T J Dhilip Kumar
Keyword(s):  
Potential Energy ◽  
Potential Energy Surface ◽  
Ab Initio ◽  
Cross Sections ◽  
Energy Surface ◽  
Molecular Ions ◽  
Basis Set ◽  
Rate Coefficients ◽  
Close Coupling ◽  
Collisional Rate Coefficients

ABSTRACT Molecular ions play an important role in the astrochemistry of interstellar and circumstellar media. C3H+ has been identified in the interstellar medium recently. A new potential energy surface of the C3H+–He van der Waals complex is computed using the ab initio explicitly correlated coupled cluster with the single, double and perturbative triple excitation [CCSD(T)-F12] method and the augmented correlation consistent polarized valence triple zeta (aug-cc-pVTZ) basis set. The potential presents a well of 174.6 cm−1 in linear geometry towards the H end. Calculations of pure rotational excitation cross-sections of C3H+ by He are carried out using the exact quantum mechanical close-coupling approach. Cross-sections for transitions among the rotational levels of C3H+ are computed for energies up to 600 cm−1. The cross-sections are used to obtain the collisional rate coefficients for temperatures T ≤ 100 K. Along with laboratory experiments, the results obtained in this work may be very useful for astrophysical applications to understand hydrocarbon chemistry.

scholarly journals Calibration of Radiocarbon Dates for the Late Pleistocene Using U/Th Dates on Stalagmites

Radiocarbon ◽  
1997 ◽  
Vol 39 (1) ◽  
pp. 27-32 ◽  
Author(s):  
John C. Vogel ◽  
Joel Kronfeld
Keyword(s):  
South Africa ◽  
Magnetic Dipole ◽  
Satisfactory Agreement ◽  
Late Pleistocene ◽  
Calibration Curve ◽  
Dipole Field ◽  
Radiocarbon Dates ◽  
The Past ◽  
The Earth ◽  
Magnetic Dipole Field

Twenty paired 14C and U/Th dates covering most of the past 50,000 yr have been obtained on a stalagmite from the Cango Caves in South Africa as well as some additional age-pairs on two stalagmites from Tasmania that partially fill a gap between 7 ka and 17 ka ago. After allowance is made for the initial apparent 14C ages, the age-pairs between 7 ka and 20 ka show satisfactory agreement with the coral data of Bard et al. (1990, 1993). The results for the Cango stalagmite between 25 ka and 50 ka show the 14C dates to be substantially younger than the U/Th dates except at 49 ka and 29 ka, where near correspondence occurs. The discrepancies may be explained by variations in 14C production caused by changes in the magnetic dipole field of the Earth. A tentative calibration curve for this period is offered.

Plant leaf recognition with shallow and deep learning: A comprehensive study

2020 ◽  
Vol 24 (6) ◽  
pp. 1311-1328
Author(s):  
Jozsef Suto
Keyword(s):  
Machine Learning ◽  
Plant Species ◽  
Research Area ◽  
Research Papers ◽  
Plant Leaf ◽  
Leaf Characteristics ◽  
The Past ◽  
The Earth ◽  
Test Sets ◽  
Comprehensive Study

Nowadays there are hundreds of thousands known plant species on the Earth and many are still unknown yet. The process of plant classification can be performed using different ways but the most popular approach is based on plant leaf characteristics. Most types of plants have unique leaf characteristics such as shape, color, and texture. Since machine learning and vision considerably developed in the past decade, automatic plant species (or leaf) recognition has become possible. Recently, the automated leaf classification is a standalone research area inside machine learning and several shallow and deep methods were proposed to recognize leaf types. From 2007 to present days several research papers have been published in this topic. In older studies the classifier was a shallow method while in current works many researchers applied deep networks for classification. During the overview of plant leaf classification literature, we found an interesting deficiency (lack of hyper-parameter search) and a key difference between studies (different test sets). This work gives an overall review about the efficiency of shallow and deep methods under different test conditions. It can be a basis to further research.

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