This review deals with quantitative descriptions of electronic transitions in atom-atom and ion-atom collisions. In one type of description, the nuclear motion is treated classically or semiclassically, and a wave function for the electrons satisfies a time-dependent Schr\"odinger equation. Expansion of this wave function in a suitable basis leads to time-dependent coupled equations. The role played by electron-translation factors in this expansion is noted, and their effects upon transition amplitudes are discussed. In a fully quantum-mechanical framework there is a wave function describing the motion of electrons and nuclei. Expansion of this wave function in a basis which spans the space of electron variables leads to quantum-mechanical close-coupled equations. In the conventional formulation, known as perturbed-stationary-states theory, certain difficulties arise because scattering boundary conditions cannot be exactly satisfied within a finite basis. These difficulties are examined, and a theory is developed which surmounts them. This theory is based upon an intersecting-curved-wave picture. The use of rotating or space-fixed electronic basis sets is discussed. Various bases are classified by Hund's cases (a)-(e). For rotating basis sets, the angular motion of the nuclei is best described using symmetric-top eigenfunctions, and an example of partial-wave analysis in such functions is developed. Definitions of adiabatic and diabatic representations are given, and rules for choosing a good representation are presented. Finally, representations and excitation mechanisms for specific systems are reviewed. Processes discussed include spin-flip transitions, rotational coupling transitions, inner-shell excitations, covalent-ionic transitions, resonant and near-resonant charge exchange, fine-structure transitions, and collisional autoionization and electron detachment.

/pdf/theory-of-electronic-transitions-in-slow-atomic-collisions-1u3ygpwoek.pdf

Theory of electronic transitions in slow atomic collisions

As the scope of quantum chemistry broadened from the consideration of stable molecules near equilibrium to encompass potential curves and surfaces, transition states, radicals, ions, and excited states, the shortcomings of the Hartree— Fock (HF) approximation for the description of the electronic structure of molecular systems became increasingly evident. The energy error of the restricted HF wave function, i.e., the difference between the HF limit energy (which is the limit approached by restricted self-consistent field calculations as the basis set approaches completeness) and the exact solution of the nonrelativistic Schrodinger equation, has been termed the correlation energy.(1) It reflects the fact that the HF Hamiltonian contains the average, rather than instantaneous, interelectron potential, and thus neglects the correlation between the motions of the electrons.

The Method of Configuration Interaction

The spin-coupled (SC) theory of molecular electronic structure is introduced as the modern development of classical valence bond (VB) theory. Various important aspects of the SC wave function are described. Attention is particularly focused on the construction and properties of different sets of N-electron spin function in different spin bases, such as the Kotani, Rumer and Serber. Applications of the SC description to a range of different kinds of chemical problems are presented, beginning with simple examples: the H2 and CH4 molecules. This is followed by the description offered by the SC wave function of more complex situations such as the insertion reaction of H2 into CH2(1A1), the phenomenon of hypervalence as displayed by molecules such as diazomethane, CH2N2, SF6 and XeF2. The SC description of the ground and excited states of benzene is briefly surveyed. This is followed by the SC description of antiaromatic systems such as C4H4 and related molecules.

/pdf/modern-valence-bond-theory-2oa0z08ns8.pdf

Modern valence bond theory

Cross sections and rate coefficients are provided for inelastic collision processes of electrons and protons with CxHy and CxHy+ (x=2,3; 1⩽y⩽2x+2) hydrocarbon species in a wide range of collision energies and plasma (gas) temperatures The considered processes include electron-impact ionization and dissociation of CxHy, dissociative excitation, ionization and recombination of CxHy+ with electrons, and both charge transfer and atom exchange in proton channels are considered separately The presented cross sections are based upon a critical assessment of available experimental data and upon an extensive use of a number of semi-empirical, physically well grounded cross section scaling relationships Information is also provided for the energetics of each individual reaction channel The cross sections and rate coefficients are presented in compact analytic forms

Collision processes of C2,3Hy and C2,3Hy+ hydrocarbons with electrons and protons

The critical fusion reactor design issue of tritium codeposition in tokamaks with carbon as wall material is closely linked with the plasma chemistry involving hydrocarbons. A complete set of cross sections for all important electron- and proton-impact processes with CHy (y=1–4) hydrocarbon impurities and their ions CHy+ is presented. The cross sections are derived on the basis of most recent experimental information and well established cross section scaling relationships. The cross sections are presented in closed analytic forms convenient for implementation in plasma simulation codes.

/pdf/collision-processes-of-chy-and-chy-hydrocarbons-with-plasma-8hjwab674w.pdf

Collision processes of CHy and CHy+ hydrocarbons with plasma electrons and protons

Ab initio calculations have been performed for states of C${\mathrm{H}}^{+}$ which arise from atomic ${\mathrm{C}}^{+}(^{2}P)$ and $\mathrm{H}(^{2}S)\ensuremath{-}X^{1}\ensuremath{\Sigma}^{+}$, $A^{1}\ensuremath{\Pi}$, $^{3}\ensuremath{\Pi}$, and $^{3}\ensuremath{\Sigma}^{+}$. Potential curves have been constructed over a wide range of internuclear distances. All computed energies are believed to be within 1 eV of their exact nonrelativistic Born-Oppenheimer value, and all energy differences are believed to have an accuracy of better than 0.3 eV. Results, with known experimental values in parentheses, are ${R}_{e}(X^{1}\ensuremath{\Sigma}^{+})=2.136$ (2.137) a.u.; ${D}_{e}^{0}(X^{1}\ensuremath{\Sigma}^{+})=4.11$ (4.21) eV; ${R}_{e}(A^{1}\ensuremath{\Pi})=2.232$ (2.333) a.u.; ${T}_{e}(X\ensuremath{-}A)=24970$ (24146) ${\mathrm{cm}}^{\ensuremath{-}1}$; ${R}_{e}(^{3}\ensuremath{\Pi})=2.130$ a.u. No evidence is found for a quasibound $^{3}\ensuremath{\Sigma}^{+}$ Rydberg state, although such behavior has been predicted for isoelectronic BH.

Calculated Potential-Energy Curves for CH +

Numerical spin-unrestricted Hartree-Fock (SUHF) wave functions have been computed for the neutral open-shell atoms Li to Br and the transition-metal ions ${\mathrm{Sc}}^{2+}$ to ${\mathrm{Cu}}^{2+}$. These wave functions have been used to obtain accurate values of the SUHF spin densities. These calculations are used to make a critical review of the numerical accuracy of previously reported SUHF spin densities and to compare our accurate values of the SUHF spin densities with those extracted from experimental data. A large majority of previous SUHF calculations have been performed using the analytic-expansion method. The spin density at the origin computed from analytic-expansion calculations is sensitive to the choice of basis functions, and it is very difficult to obtain a precise measure of its accuracy. Our numerical SUHF calculations yield the SUHF value of the spin density $\ensuremath{\chi}$ to an accuracy conservatively estimated to be \ifmmode\pm\else\textpm\fi{}0.01 a.u. Comparison with analytic-expansion calculations indicates that the use of large, carefully selected basis sets usually yields spin densities within 20% of the numerical SUHF values reported here. The calculated SUHF spin densities are compared with available experimental values and it is found that (a) for the alkali atoms Li, Na, and K, the SUHF spin densities are 97, 86, and 77% of experiment; (b) for the first-row atoms N,O, and F, the SUHF spin densities are 193, 172, and 186% of experiment; (c) the SUHF spin density for P is opposite in sign and 153% of the absolute value of the experimental spin density; (d) the SUHF spin densities of the $4{s}^{2}3{d}^{n}$ transition-metal atoms Ti, V, Mn, and Co are 82, 75, 72, and 67% of experiment; and (e) the SUHF spin density of As is 231% of experiment. It is concluded that, although some correlations are possible between SUHF and experimental values, the SUHF method should be used with extreme caution for the prediction of spin densities at the origin. This work provides a guide to the reliability of the SUHF predictions.

Study of the Contact-Term Contribution to the Hyperfine Structure Obtained from Spin-Unrestricted Hartree-Fock Wave Functions

Self-consistent-field (SCF) calculations have been used to determine the ground negative-ion and ground neutral potential-energy curves for HeH, ArH, and ArCl. In the systems studied, the $X^{1}\ensuremath{\Sigma}$ potential of the negative-ion state is more repulsive at intermediate internuclear separations than the $X^{2}\ensuremath{\Sigma}$ potential of the neutral partners, leading to a curve crossing of the negative-ion state into the continuum. However, at small internuclear separations the negative-ion potential becomes less repulsive than the neutral potential, leading to a second curve crossing out of the continuum. The calculated potential-energy curves are used to provide estimates of the energy thresholds and cross sections for electron detachment in the collisions ${\mathrm{H}}^{\ensuremath{-}}$ + He, ${\mathrm{H}}^{\ensuremath{-}}$ + Ar, and ${\mathrm{Cl}}^{\ensuremath{-}}$ --Ar. The angular thresholds for electron detachment in differential-scattering measurements are also given and compared to experimental data.

Self-consistent-field potential energies for the ground negative-ion and neutral states of HeH, ArH, and ArCl

THE first unidentified interstellar microwave line was reported in 1970 by Buhl and Snyder1, who, appropriately enough, named this line the X-ogen line. They were originally1 able to detect X-ogen at 89.190±0.002 GHz in five galactic sources: W3 (OH), Orion, L134, Sgr A (NH3A) and W51. The first two candidates suggested for X-ogen were HNC and HCO+, the former the suggestion of Herzberg (noted by Buhl and Snyder1) and the latter that of Klemperer2. Since then Snyder and Buhl3 have concluded that a second unidentified line (at 90.665 GHz) is more likely to be due to HNC and very recent ab initio calculations4 have unquestionably ruled out HNC as a candidate for X-ogen.

Theoretical Support for the Assignment of X-ogen to the HCO+ Molecular Ion

https://escholarship.org/content/qt0wb910fk/qt0wb910fk.pdf?t=p0uv7i

Theoretical dipole moment function of the X1Σ+ state of HI

Handle everyday research tasks with reliable, citation-backed results

Your personal Research Agent to handle research tasks with citation-backed results

Popular Tasks used by Researchers

How can I help with your research?

Meet SciSpace

Get more enhanced response by uploading the PDFs you want me to reference.

No relevant PDFs in your library

SciSpace is the AI research assistant for academics. Run systematic literature reviews on 280M+ papers, and write papers with cited sources. Trusted by 1M+ students, PhDs & researchers.

SciSpace | AI for Research

Analyze PDFs

Code & Manuscripts

Funding & Grants

Literature & Patents

Medical & Clinical Data

Systematic Review

Visualize & Present

Web & Data

Build a Google Scholar-like website for your research.

Build a website

Create charts and images for your research

Create a Chart

Write a paper for submission to a journal

Draft a manuscript

Patent Search

Design eye-catching scientific posters in minutes.

Scientific Poster Generation

Systematic Literature Review

One task is running at the moment. Your messages will be shown right after.

Drag and drop or click here to browse

Loved by <highlight>1 million+</highlight> researchers

Extract a list of specific topics and their sources from unstructured text

Topics

Compare and analyze relevant papers that matches with your search

Papers

Get insights from PDFs and bookmarked papers from your library

My library

Recent searches

Try searching for:

Catch AI-generated content in scholarly and non-scholarly content

{ai} Detector

Ai Writer

Get PDF Summaries, highlighted text explanations 

Chat with PDF

Effortlessly create in-text citations and bibliographies in APA and 2,500 other formats

Citation generator

Get explanations, summaries, and answers on academic papers

Ease up your research workflow with {scispace}'s cohort of exciting AI tools

Elevate your academic writing skills and convey your ideas the way you want

Paraphraser

Explore our range of reading and writing tools

Your file is being prepared and should be ready in a few minutes. If it's a large file, it might take a bit longer. You can close this window, and we'll email you the file when it's done.

You have reached a maximum limit of <strong>{limit}</strong> columns in the table. Remove at least <strong>1</strong> column to add or create another one.

B. Liu

Author Tools

Chat about Author