scholarly journals Low-temperature chemistry using the R-matrix method

2016 ◽  
Vol 195 ◽  
pp. 31-48 ◽  
Author(s):  
Jonathan Tennyson ◽  
Laura K. McKemmish ◽  
Tom Rivlin
Keyword(s):  
Cross Sections ◽  
Potential Energy Surfaces ◽  
Collision Energy ◽  
Molecular Spectra ◽  
Matrix Formalism ◽  
Ultracold Molecules ◽  
R Matrix ◽  
Deep Wells ◽  
Variational Calculations ◽  
Ultracold Collision

Techniques for producing cold and ultracold molecules are enabling the study of chemical reactions and scattering at the quantum scattering limit, with only a few partial waves contributing to the incident channel, leading to the observation and even full control of state-to-state collisions in this regime. A new R-matrix formalism is presented for tackling problems involving low- and ultra-low energy collisions. This general formalism is particularly appropriate for slow collisions occurring on potential energy surfaces with deep wells. The many resonance states make such systems hard to treat theoretically but offer the best prospects for novel physics: resonances are already being widely used to control diatomic systems and should provide the route to steering ultracold reactions. Our R-matrix-based formalism builds on the progress made in variational calculations of molecular spectra by using these methods to provide wavefunctions for the whole system at short internuclear distances, (a regime known as the inner region). These wavefunctions are used to construct collision energy-dependent R-matrices which can then be propagated to give cross sections at each collision energy. The method is formulated for ultracold collision systems with differing numbers of atoms.

scholarly journals ELASTIC BACKSCATTERED CROSS-SECTIONS OF 14N(P,P0)14N AT HIGH ANGLES

2020 ◽  
Vol 20 (3) ◽  
pp. 749-754
Author(s):  
MOHAMED ELTAYEB M. EISA ◽  
JOHAN ANDRE MARS ◽  
MUSTAFA J. ABUALREISH ◽  
MARWA L. WAREGH
Keyword(s):  
Cross Section ◽  
Cross Sections ◽  
Ion Beam ◽  
Region Of Interest ◽  
Laboratory Frame ◽  
Matrix Formalism ◽  
Cross Section Data ◽  
R Matrix ◽  
Section Data ◽  
Elastic Backscattering

The importance and present needs of proton cross section data of nitrogen needed by the Ion Beam Analysis (IBA) community are briefly reviewed. Previous experimental data presently used for the theoretical determination of the proton cross-sections are discussed. The Azure code based on the R-matrix formalism was then used to evaluate the data and to determine the nitrogen cross section in the previous and presently desired angular domain and energy region of interest. The experimental elastic backscattering cross section data, as spectra, for back-scattering analysis determined at angles in the laboratory frame of reference, θi,lab, of 165o, 170o and 176o are presented.

scholarly journals Developments regarding three-body reaction channels within the R-matrix formalism

2020 ◽  
Vol 239 ◽  
pp. 03002
Author(s):  
Benedikt Raab ◽  
Thomas Srdinko ◽  
Helmut Leeb
Keyword(s):  
Cross Sections ◽  
Matrix Theory ◽  
Resonance Region ◽  
Reaction Cross ◽  
Resonance Structure ◽  
Matrix Formalism ◽  
Matrix Formulation ◽  
R Matrix ◽  
Reaction Channels ◽  
Three Body

At low incident energies of nucleon-induced reaction cross sections exhibit a striking resonance structure which cannot properly be described by (semi-) microscopic models. Usually R-matrix theory is applied which provides a sufficiently accurate but phenomenological description of the resonance region. However, standard R-matrix theory is only suited for two-particle channels. Three- and many-particle channels which may occur at rather low incident energies and are usually treated in approximative or effective way. In this contribution an extension to unequal masses of the R-matrix formulation of Glockle based on the Faddeev equation is performed and proper expressions for numerical implementation are given.

scholarly journals Multi-photon above threshold ionization of multi-electron atoms and molecules using the R-matrix approach

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Jakub Benda ◽  
Zdeněk Mašín
Keyword(s):  
Cross Sections ◽  
Outer Region ◽  
Angular Distributions ◽  
Matrix Formalism ◽  
Computationally Efficient ◽  
Threshold Ionization ◽  
R Matrix ◽  
Atoms And Molecules ◽  
Above Threshold Ionization ◽  
Transition Matrix Elements

AbstractWe formulate a computationally efficient time-independent method based on the multi-electron molecular R-matrix formalism. This method is used to calculate transition matrix elements for the multi-photon ionization of atoms and molecules under the influence of a perturbative field. The method relies on the partitioning of space which allows us to calculate the infinite-range free-free dipole integrals analytically in the outer region, beyond the range of the initial bound wave function. This approach is valid for an arbitrary order, that is, any number of photons absorbed both in the bound and the continuum part of the spectrum (below- and above-threshold ionization). We calculate generalized multi-photon cross sections and angular distributions of different systems (H, He, $$\hbox {H}_{{2}}$$ H 2 , $$\hbox {CO}_{{2}}$$ CO 2 ) and validate our approach by comparison with data from the literature.

INVESTIGATION OF THE CONTRIBUTION FOR THE NONCOLLINEAR CHANNEL OF THE F(2P3/2,2P1/2) + H2/D2 REACTIONS ON FOUR DIABATIC POTENTIAL ENERGY SURFACES

2012 ◽  
Vol 11 (03) ◽  
pp. 561-571 ◽  
Author(s):  
TING-XIAN XIE
Keyword(s):  
Potential Energy ◽  
Barrier Height ◽  
Cross Sections ◽  
Rate Constants ◽  
Potential Energy Surfaces ◽  
Collision Energy ◽  
Higher Temperature ◽  
The Difference ◽  
Lower Temperature ◽  
Energy Surfaces

We performed the nonadiabatic time-dependent wave packet calculation on the four diabatic potential energy surfaces, which have the different barrier height, to investigate the contribution of the noncollinear channel for the F (2P) + H2/D2 (v = j = 0) reactions. The reaction probabilities, integral cross-sections, and rate constants are presented. The results indicate that the probabilities as the function of the collision energy have an obvious translation. The reactive activity of the reactions comes from the noncollinear reactive channel. The bent barrier height would decrease the reactive activity. The integral cross-sections are in the order of AWS < LWA-5 < LWA-78 ≈ MASW, which is opposite to that of the bent barrier height. At the lower temperature, the difference of the rate constants is unambiguous. As the temperature increases, the difference reduces. At the higher temperature, the rate constants computed on the four potential energy surfaces are close.

scholarly journals Relativistic B-Spline R-Matrix Calculations for Electron Collisions with Ytterbium

Atoms ◽  
2021 ◽  
Vol 9 (3) ◽  
pp. 47
Author(s):  
Kathryn R. Hamilton ◽  
Klaus Bartschat ◽  
Oleg Zatsarinny
Keyword(s):  
Experimental Data ◽  
Electron Scattering ◽  
Cross Sections ◽  
Matrix Method ◽  
Model Potential ◽  
Electron Collisions ◽  
R Matrix ◽  
B Spline ◽  
Potential Approach

We have applied the full-relativistic Dirac B-Spline R-matrix method to obtain cross sections for electron scattering from ytterbium atoms. The results are compared with those obtained from a semi-relativistic (Breit-Pauli) model-potential approach and the few available experimental data.

scholarly journals Photoionization Cross-Sections of Carbon-Like N+ Near the K-Edge (390–440 eV)

Atoms ◽  
2021 ◽  
Vol 9 (2) ◽  
pp. 27
Author(s):  
Jean-Paul Mosnier ◽  
Eugene T. Kennedy ◽  
Jean-Marc Bizau ◽  
Denis Cubaynes ◽  
Ségolène Guilbaud ◽  
...  
Keyword(s):  
High Resolution ◽  
Cross Section ◽  
Cross Sections ◽  
Experimental Studies ◽  
Photoionization Cross Section ◽  
Theoretical Work ◽  
Rydberg Series ◽  
R Matrix ◽  
Resonance Strengths ◽  
Nitrogen Ion

High-resolution K-shell photoionization cross-sections for the C-like atomic nitrogen ion (N+) are reported in the 398 eV (31.15 Å) to 450 eV (27.55 Å) energy (wavelength) range. The results were obtained from absolute ion-yield measurements using the SOLEIL synchrotron radiation facility for spectral bandpasses of 65 meV or 250 meV. In the photon energy region 398–403 eV, 1s⟶2p autoionizing resonance states dominated the cross section spectrum. Analyses of the experimental profiles yielded resonance strengths and Auger widths. In the 415–440 eV photon region 1s⟶(1s2s22p2 4P)np and 1s⟶(1s2s22p2 2P)np resonances forming well-developed Rydberg series up n=7 and n=8 , respectively, were identified in both the single and double ionization spectra. Theoretical photoionization cross-section calculations, performed using the R-matrix plus pseudo-states (RMPS) method and the multiconfiguration Dirac-Fock (MCDF) approach were bench marked against these high-resolution experimental results. Comparison of the state-of-the-art theoretical work with the experimental studies allowed the identification of new resonance features. Resonance strengths, energies and Auger widths (where available) are compared quantitatively with the theoretical values. Contributions from excited metastable states of the N+ ions were carefully considered throughout.

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