Atomic Lithium Excitation by Electron Impact

Abstract

Article history: Received:14 JUN, 2019 Accepted: 25 AUG, 2019 Available Online: 25 DEC, 2019 Bethe approximation had been used to compute the excitation cross section in term of the diploe oscillator strength for some allowed transitions between energy levels of Li-atom collide with electrons with impact energy range (2-2000) eV. We also compute the radiation transition probability and lifetime. Our results for all calculations we had done were compared with the available theoretical and experimental data. DOI: http://dx.doi.org/10.31257/2018/JKP/2019/110205 K e y w o r d s : Excitation Cross section Lithium atom Electron impact Bethe approximation نورتكللاا ريثأتب مويثيللا ةرذ ةراثا فلخ نسحلا دبع ءلاع نسحلا دبع ىفطصم بابر ءايسيفلا نسق مىلعلا تيلك ةرصبلا تعهاج :تيحاخفولا ثاولكلا لا ــــ خ ـــ صلا ـــ ت ةراثأ يضرع عطقه مىيثيللا ةرذ ىورخكللإا ريثأح ثيب بيرقح بميرقح مامخخمتا نمح Bethe يم ةرامثرل يمضرعلا عمطقولا امسحل ممح بمببه ةىمق ييامٌث بطقلا لاا ضعبل ثلااقخً يمه تمقاطلا ثايىخسه ييب اهب حىوسولا ممٌع مىميثيللا ةرذ همامصح اه عمه ريثأممخلا تممقا يمممه ثاذ ثاممًورخكللإا (2-2000) eV. و لاوخحا امم يأ بممسحً تممي لاا اممقخً عاعمشلإا ي و امقخًلاا يمهز ثامًايبلا عمه امااٌيرجأ يمخلا ثابامسحلا عميولل امٌلياخً تمًراقه جموح . تحاخولا تيبيرلخلاو تيرظٌلا . JOURNAL OF KUFA–PHYSICS | Vol. 11, No. 2 (2019) Rabab M. Abdul Hassan, Alaa A. Khalaf 30 oscillator strength for these lines done by Fock and Petrashen [2], where they used in their treatment the wave functions of self-consistent field. Also the excitation cross section is performed by Williams et. al [3], where they calculate the excitation cross section at a limited number of electron impact energies. In the experimental side, Leep and Gallagher [4], Zajonc and Gallagher [5] were measured the excitation cross section for 2s-state to 2p-state for neutral lithium collide with electrons. The importance of studying inelastic scattering is coming from that the need is increasing for reliable and accurate computational cross section data in many fields like astrophysics, physics of radiation, and plasma physics [6]. In the inelastic interactions of neutral atoms -in ground and excited stateswith electrons, the information of cross sections are very important and has fundamental interest. A database of theoretical cross sections for inelastic collision of lithium atoms with electrons in the ground and excited states have been proposed by Schwinzer et. al [7]. To derive accurate cross sections for all inelastic excitation processes for lithium atoms colliding with single electrons they used sophisticated theoretical methods of calculations. The results of these methods were tested critically against the available newest experimental measurements data. The computation of atomic transition probabilities for allowed electric dipole lines of Li-atom, were performed by Wiese et. al [8]. The critical data compilations were included transitions between ground state and some excited states and between excited states itself. The wave functions of Hartree-Fock for 2s, 2p, 3s, 3p, and 3d states of Li-atom were computed by a wide-range method. The followed procedure represented by depend the method of analytic self-consistent field. Oscillator strengths for some transitions between these states were calculated using the dipole length formula. In this paper, Bethe approximation which play as a correct for the behavior of the Born approximation at high energies was used to calculate the excitation cross section for the scattering of electrons from lithium atom. The generated cross section is based on the calculated oscillator strength which in turn was produced from the given Hartree-Fock wave functions. Also we calculate the transition probability and lifetime between the states under investigation. Our results for all the preceding calculations were compared with available theoretical and measurements data, and in general the comparison was good 2. THEORY In the excitation process for atoms by fast electrons from its initial (i) state to final (f) or excited state. The integral cross section which performed using Born approximation where the generalized oscillator strength (GOS) plays a crucial role [9-10], can be expressed as: