Veza potencijalnog i izmenskog raspršenja u sporim sudarima iona i atoma

The effect of the direct interaction in a slow ion-atom collision on the exchange amplitude is considered. A modified formula is obtained for the AH-A resonant charge exchange cross section and calculations are made for the case of A being an inert gas atom. The polarization (ion) capture radius and the elastic scattering cross section are estimated at thermal energies.Razmotren je uticaj direktne interakcije na amplitudu izmene u sporim sudarima iona i atoma. Za A2+ - A rezonantnu izmenu naelektrisanja dobivena je modifikovana formula preseka uzimajući u obzir ovaj uticaj. Kada je A atom inertnog gasa, izvršena su izračunavanja preseka po ovoj formuli. Procenjene su vrednosti radiusa polarizacionog zahvata i elastični preseci pri ovim sudarima u termalnoj oblasti energija

Cross sections for 14-eV e-H2 resonant collisions: Dissociative electron attachment

The dissociative electron attachment (DEA) process in electron-H[sub]2 molecule collisions, involving the ^2Σ^+[sub]g excited electronic Rydberg state of molecular hydrogen ion H[sub]2^−, is investigated theoretically. The DEA cross section has been calculated within the local complex potential approximation. The convoluted cross section, which presents a peak located at the incident energy of about 14 eV, compares favorably with available experimental data

Cross sections for 11–14-eV e-H2 resonant collisions: Vibrational excitation

Resonant vibrational excitation (RVE) cross sections have been calculated for the electron-H2 molecule collisions in the energy range 11–14 eV involving the 2Σ+g excited electronic state of the molecular hydrogen ion H2−. This state, whose threshold is located around 14 eV, gives rise to the so-called series a of the observed peaks in electron-impact differential cross-section measurements. The calculations have been performed within the local complex potential approximation by using the available theoretical potential energy and width for the 2Σ+g resonant state. The cross sections for all vi=0→vf=1–14 RVE transitions have been calculated. A satisfactory agreement of calculated cross sections with the available experimental data is obtained

Electron-impact vibrational excitation of vibrationally excited H2 molecules involving the resonant 2(Sigma)g+ Rydberg-excited electronic state

Electron-impact theoretical cross sections and rate coefficients for vibrational excitation of vibrationally excited H2 molecules, occurring through the H−2 resonant species in the 2Σ+g Rydberg-excited electronic state, are presented. The cross sections are calculated as functions of the incident electron energy by adopting the local-complex-potential model for resonant collisions and by using ab initio calculated molecular potentials and resonance widths. The calculations have been extended to all possible vibrational transitions linking all 15 vibrational levels of the electronic ground state of the H2 molecule. The corresponding rate coefficients are also obtained as a function of the electron temperature by assuming a Maxwellian electron energy distribution function, and a simple analytical expression is derived. Finally, the present rate coefficients for the transitions starting from the lowest vibrational level of the H2 molecule are compared with those for the process involving the X2Σ+u resonant state of the H−2 molecular ion

Electron impact induced allowed transitions between triplet states of H2

Electron-impact-induced excitation and dissociation processes between the excited triplet states a (3)Sigma(g)(+)-->d (3)Pi(u), c (3)Pi(u)-->h (3)Sigma(g)(+), and c (3)Pi(u)-->g (3)Sigma(g)(+) of molecular hydrogen are studied by using the impact-parameter method. The cross sections for nu(i)-nu(f) resolved vibronic transitions between states have been calculated in the energy range from threshold to 100 eV; their maxima being located in the region of 5-10 eV. A special treatment was required for the transition to the h (3)Sigma(g)(+) state, whose adiabatic potential-energy curve possesses a barrier at the internuclear distance of about 5a(0), sustaining three quasi-bound vibrational states with widths of 5.3x10(-12), 1.5x10(-3), and 42.0 cm(-1), respectively. The quasistationary character of these vibrational states is taken into account when calculating the c (3)Pi(u)-->h (3)Sigma(g)(+) excitation and dissociation cross sections

Electron Impact Ionization Close to the Threshold: Classical Calculations

In this paper we present Classical Trajectory Monte Carlo (CTMC) calculations for single and multiple electron ionization of Argon atoms and ions in the threshold region. We are able to recover the Wannier exponents a for the power-law behavior of the cross section s versus excess energy: the exact value of the exponent as well as the existence of its saturation for multiple ionization appear to be related to how the total binding energy is shared between target electrons.Comment: 9 pages. To be published in Journal of Physics

Multiple ionization of rare gases by hydrogen-atom impact

Cross sections for the multiple ionization of He, Ne, Ar, and Kr by H^0 impact with and without the simultaneous ionization (electron loss) of the projectile are presented in the energy range 75–300 keV. The data were measured by coincident detection of the recoil target ions and the charge-state analyzed scattered projectiles. To obtain information about the role played by the electron of H^0 in the collision, the measurements were repeated with protons under the same experimental conditions. The measured data are analyzed using the classical trajectory Monte Carlo (CTMC) method. CTMC describes well the experimental data for both projectiles for single vacancy creation; however, increasing deviation is observed between theory and experiment with increasing number of created vacancies and with decreasing target atomic number