177,257 research outputs found
Cross sections for the two-step radiative decay process X(v) → A(v′′) → X(v′) in e-LiH collisions
No full textAbstract: The cross sections for the two-step process, represented by the electron-impact vibro-electronic excitation X1Σ+(v) → A1Σ+(v′ ′) of the LiH molecule, followed by radiative decay back on the vibrational manifold of the ground state, A1Σ+(v′ ′) → X1Σ+(v′) , are calculated as a function of the incident electron energy from the threshold to 1000 eV. The final cross sections for the two-step process, which results in an overall vibrational excitation of the molecule, known also as E-v process, are provided for all the possible v, v′ transitions among the vibrational levels, including the continuum, of the electronic ground state. Graphic abstract: [Figure not available: see fulltext.
Electron-impact cross sections for processes involving vibrationally excited diatomic hydrogen molecules
No full textElectron-impact cross sections for processes involving vibrationally excited molecules of hydrogen and its isotopes are reviewed, briefly discussing their role in negative ion plasma sources
Atom-molecule sudden theory of scattering: AB Initio corrections and range of validity of the collision model
No full textThe problem of describing atom-molecule vibro-rotational processes, within a sudden picture of scattering, is analyzed in a completely ab initio fashion. The resulting generalized infinite order sudden (GIOS) theory characteristically: (1) emphasizes the role of off-shell sudden T-matrices; (2) leads, from first principles, to corrective terms describing the influence of target motion. It is pointed out that, by means of such corrective terms, it is possible to define β(n) coefficients, related to the (ΔτrA/ΔτrBC)n power of (atomic/molecular) characteristic times for the process considered. A numerical analysis of such coefficients then leads to quantitative information on the validity of the sudden picture of energy transfer, for the process investigated. The theory is tested numerically by applying it to a collinear model of vibrational excitation
Dependence of Electron-Impact Excitation Cross-Sections on the Initial Vibrational Quantum Number in H-2 and D2 Molecules - X(1)Sigma-G+-]B(1)Sigma-U+ and X(1)Sigma-G+-]C(1)Pi-U Transitions
No full textElectron-impact excitation cross sections have been calculated using the impact-parameter method for X1SIGMA(g)+-->B1SIGMA(u)+ and X1SIGMA(g)+-->C1PI(u) transitions for both H-2 and D2 molecules as a function of incident energy and of vibrational quantum number v(i). The results show that the cross sections initially increase monotonically with increasing v(i) and follow the opposite trend for higher v(i) values
Scaling of electron-impact electronic excitation cross sections of vibrationally excited diatomic molecules
No full textA scaling law for the electron-impact electronic excitation cross sections of vibrationally excited diatomic molecules is derived and applied to the X(1) Sigma(g)(+)-->B-1 Sigma(u)(+) transitions in hydrogen and deuterium
Electron-impact state-to-state cross sections and rate coefficients for X(v)→A(v')excitation of LiH molecule
No full textElectron-impact cross sections for the v→V'transitions between the vibrational levels of X 1Σ+ and A 1Σ+ electronic states of the LiH molecule, are calculated from threshold to 1000 eV by using the threshold-modified Massey-Mott approximation. The rate coefficients for the same transitions are also calculated in the range 0.1-1000 eV. Scaling relationships for both the v - v′ cross section and v - v′ rate coefficients are derived, allowing us to represent the calculated quantities in a compact analytic form
Electron-impact dissociation cross sections of vibrationally excited He<sub>2</sub><sup>+</sup> molecular ion
No full textElectron-impact cross sections for the dissociation process of vibrationally excited He molecular ion, as a function of the incident electron energy are calculated for the dissociative transition by using the R-matrix method in the adiabatic-nuclei approximation. The potential energy curves for the involved electronic states and transition dipole moment, also calculated with the R-matrix method, were found to be in good agreement with the results reported in literature. The vibrationally resolved dissociation cross sections of He exhibit a resonant structure around 7 eV. The observed strong variation of the magnitude of this structure with the vibrational level is explained in terms of the overlap of initial and final (continuum) state wave functions in the Franck–Condon region
Electron-impact state-to-state resolved cross sections and rate coefficients for the X(v) → A(v') excitation in BeH molecules
No full textElectron-impact cross sections are calculated for the v -> v' transitions occurring between the vibrational levels of the two X-2 Sigma(+) and A(2)Pi electronic states of the BeH molecule. The calculations are performed with the R-matrix method for a purely vertical electronic transition for energies from threshold to 15 eV, and by using a modified version of the Mott and Masssey approximation to extend the calculations to high energies and to vibrational excitations. Rate coefficients are also calculated for the same transitions. The calculated v-v' selective cross sections and rate coefficients both satisfy distinct scaling relationships, which can be represented in a simple analytic for
Collective phenomena in pp and ep scattering
No full textBjorken scaling violation in deep inelastic electron-proton scattering (DIS) is related to the rise of hadronic cross sections by using the additive quark model. Of special interest is the connection between saturation in the low-x behavior of the DIS structure functions (SF) and possible slow-down of the pp cross section rise due to saturation effects. We also identify saturation effects in the DIS SF with phase transition that can be described by the Van der Waals equation of state
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