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Positronium (Ps) is a system consisting of an electron and its anti-particle, a positron, bound together into an exotic atom, specifically an onium. Unlike hydrogen, the system has no protons. The system is unstable: the two particles annihilate each other to predominantly produce two or three gamma-rays, depending on the relative spin states. The energy levels of the two particles are similar to that of the hydrogen atom. However, because of the reduced mass, the frequencies of the spectral lines are less than half of those for the corresponding hydrogen lines.
A timeline of atomic and subatomic physics.
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Electron excitation is the transfer of a bound electron to a more energetic, but still bound state. This can be done by photoexcitation (PE), where the electron absorbs a photon and gains all its energy or by collisional excitation (CE), where the electron receives energy from a collision with another, energetic electron. Within a semiconductor crystal lattice, thermal excitation is a process where lattice vibrations provide enough energy to transfer electrons to a higher energy band such as a more energetic sublevel or energy level. When an excited electron falls back to a state of lower energy, it undergoes electron relaxation (deexcitation). This is accompanied by the emission of a photon or by a transfer of energy to another particle. The energy released is equal to the difference in energy levels between the electron energy states.
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Quantemol Ltd is based in University College London initiated by Professor Jonathan Tennyson FRS and Dr. Daniel Brown in 2004. The company initially developed a unique software tool, Quantemol-N, which provides full accessibility to the highly sophisticated UK molecular R-matrix codes, used to model electron polyatomic molecule interactions. Since then Quantemol has widened to further types of simulation, with plasmas and industrial plasma tools, in Quantemol-VT in 2013 and launched in 2016 a sustainable database Quantemol-DB, representing the chemical and radiative transport properties of a wide range of plasmas.
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Collaborative Computational Project Q (CCPQ) was developed in order to provide software which uses theoretical techniques to catalogue collisions between electrons, positrons or photons and atomic/molecular targets. The 'Q' stands for quantum dynamics. This project is accessible via the CCPForge website, which contains numerous other projects such as CCP2 and CCP4. The scope has increased to include atoms and molecules in strong laser fields, low-energy interactions of antihydrogen with small atoms and molecules, cold atoms, Bose–Einstein condensates and optical lattices. CCPQ gives essential information on the reactivity of various molecules, and contains two community codes R-matrix suite and MCTDH wavepacket dynamics.
The UK Molecular R-Matrix codes are a set of software routines used to calculate the effects of collision of electrons with atoms and molecules. The R-matrix method is used in computational quantum mechanics to study scattering of positrons and electrons by atomic and molecular targets. The fundamental idea was originally introduced by Eugene Wigner and Leonard Eisenbud in the 1940s. The method uses the fixed nuclei approximation, where the molecule's nuclei are considered fixed when collision occurs and the electronic part of the problem is solved. This information is then plugged into calculations which take into account nuclear motion. The UK Molecular R-Matrix codes were developed by the Collaborative Computational Project Q (CCPQ).
References
- ↑ Kupershmidt, Boris A. (1999). "What a Classical r-Matrix Really Is". Journal of Nonlinear Mathematical Physics. Informa UK Limited. 6 (4): 448–488. arXiv: math/9910188 . Bibcode:1999JNMP....6..448K. doi:10.2991/jnmp.1999.6.4.5. ISSN 1402-9251.
- ↑ Li, Lifeng (1994-11-01). "Bremmer series, R-matrix propagation algorithm, and numerical modeling of diffraction gratings". Journal of the Optical Society of America A. The Optical Society. 11 (11): 2829–2836. Bibcode:1994JOSAA..11.2829L. doi:10.1364/josaa.11.002829. ISSN 1084-7529.
- ↑ Wigner, E. P.; Eisenbud, L. (1947-07-01). "Higher Angular Momenta and Long Range Interaction in Resonance Reactions". Physical Review. American Physical Society (APS). 72 (1): 29–41. Bibcode:1947PhRv...72...29W. doi:10.1103/physrev.72.29. ISSN 0031-899X.
- ↑ Burke, P G; Hibbert, A; Robb, W D (1971). "Electron scattering by complex atoms". Journal of Physics B: Atomic and Molecular Physics. IOP Publishing. 4 (2): 153–161. Bibcode:1971JPhB....4..153B. doi:10.1088/0022-3700/4/2/002. ISSN 0022-3700.
- ↑ Schneider, Barry (1975). "R-matrix theory for electron-atom and electron-molecule collisions using analytic basis set expansions". Chemical Physics Letters. Elsevier BV. 31 (2): 237–241. Bibcode:1975CPL....31..237S. doi:10.1016/0009-2614(75)85010-x. ISSN 0009-2614.
- ↑ Schneider, Barry I. (1975-06-01). "R-matrix theory for electron-molecule collisions using analytic basis set expansions. II. Electron-H2 scattering in the static-exchange model". Physical Review A. American Physical Society (APS). 11 (6): 1957–1962. Bibcode:1975PhRvA..11.1957S. doi:10.1103/physreva.11.1957. ISSN 0556-2791.
- ↑ C J Gillan, J Tennyson, and P G Burke, in Computational Methods for Electron-Molecule Collisions, eds. W M Huo and F A Gianturco, (Plenum, New York, 1995), p. 239
- ↑ Carr, J.M.; Galiatsatos, P.G.; Gorfinkiel, J.D.; Harvey, A.G.; Lysaght, M.A.; Madden, D.; Mašín, Z.; Plummer, M.; Tennyson, J. (2012). "The UKRmol program suite". Eur. Phys. J. D (66): 58. doi:10.1140/epjd/e2011-20653-6.
- ↑ Mašín, Zdeněk; Benda, Jakub; Gorfinkiel, Jimena D.; Harvey, Alex G.; Tennyson, Jonathan (2019-12-07). "UKRmol+: A suite for modelling electronic processes in molecules interacting with electrons, positrons and photons using the R-matrix method". Computer Physics Communications. 249: 107092. arXiv: 1908.03018 . doi:10.1016/j.cpc.2019.107092.