Proton Impact Excitation Research Articles

Differential and total cross sections for proton impact excitation of He

An extended form of the Vainshtein-Presnyakov-Sobelman approximation is used to calculate differential and total cross sections for proton impact excitation of the n = 2 level in He. Agreement with experiment is very good.

Angular differential cross sections for excitation of atomic hydrogen to then=2level by proton impact

Differential cross sections for 15-145-keV proton impact excitation of atomic hydrogen to the n = 2 level have been determined for center-of-mass scattering angles 0 to 1.2 mrad. The cross sections were obtained from an analysis of the angular distribution of protons which had lost an energy corresponding to the excitation of atomic hydrogen to its n = 2 level. The differential cross sections obtained are in rather good agreement with available coupled-state calculations as well as the simpler Glauber-approximation calculations. However, at the larger scattering angles the cross sections obtained from the theoretical treatments appear to decrease more rapidly than the experimental data.

Calculation of proton-impact excitation of helium using the Glauber approximation

Cross sections for the $1^{1}S\ensuremath{\rightarrow}n^{1}S$ ($n=2,3,4$) excitations of atomic helium under proton impact are calculated with incident energy ranging from 25 to 1000 keV employing the Glauber approximation. A properly orthogonalized set of He wave functions are used. The generalized oscillator strengths for $1^{1}S\ensuremath{\rightarrow}2^{1}S$ and $1^{1}S\ensuremath{\rightarrow}3^{1}S$ excitations are also calculated with these wave functions, and the results are compared with the existing theoretical and experimental data. The full Glauber scattering amplitude is separated into single-and double-scattering parts. The single-scattering amplitude is evaluated from a closed-form expression. A numerical method is employed to calculate some integrals occuring in the double-scattering amplitude. At incident energies above 500 keV, the single-scattering contribution is found to dominate the Glauber result. The effect of the double-scattering term is appreciable at intermediate energies, where it substantially lowers the cross sections from the corresponding single-scattering result. The Glauber result at intermediate energies also underestimates most of the existing theoretical and experimental cross sections, which already show a wide variation among themselves in absolute values. However, the functional dependence of the Glauber cross sections on energy is similar to that depicted by other calculations and measurements. Furthermore, the average ratio of the Glauber cross sections for $3^{1}S$ and $4^{1}S$ excitations at high energies show reasonable agreement with those obtained from other theories, as also from the ${n}^{\ensuremath{-}3}$ law of cross sections.

Proton impact excitation of the low lying autoionizing levels in the heavier alkali atoms

The total cross-section for proton impact excitation of some low lying autoionizing levels in alkali metal atoms have been calculated using Born approximation. Hartree-Fock atomic orbitals appropriate for the initial and final orbitals have been used. The results are compared with the other available theoretical calculations.

The excitation of near-UV emission by H+, H°, and He+impact on CO2and N2O at 0.7-10 keV

Emission spectra in the 2850- to 4300-A region produced by 0.7- to 10-keV impact of H+, H°, and He+ on CO2 and N2O have been observed. The emission consists almost exclusively of the A-X and B-X systems of CO2+ and the A-X system of N2O+. There are no emissions from excited fragments of the parent molecules. Cross sections for proton impact excitation reach maxima of 1–4 × 10−16 cm² in the collision energy range observed. Cross sections for H° excitation reach maxima of 0.4–1 × 10−16 cm².

Quantum theory of proton collisions with ions of np2configuration. Application to Fe+12

Proton impact excitation of positive ions is investigated using the quantum approach of the close-coupling method. The theory is applied to fine structure transitions of atoms with np2 configurations. Results are presented for the 3P0 to 3P1, 3P0 to 3P2 and 3P1 to 3P2 transitions in Fe+12 and are compared with those obtained by other methods at low and high energies.

Proton excitation of neon

The first-order distortion method is used to calculate the cross section for proton impact excitation of neon to levels of the 2p53s and 2p53p configurations. The results are compared with the proton energy loss measurements of York et al. (1972). The distortion method shows considerable improvement over the first Born cross sections in the energy range up to 200 keV. A solution of the coupled equations for the scattering problem within a set of initially degenerate sub-states gives a negligible improvement of the distortion result for the total cross section.

Proton collisional excitation in the ground configuration of Fe+12, II

Improved values of the proton impact excitation cross sections at coronal energies for all the Fe+12 ground configuration (3s23p2) transitions are presented. These were obtained by direct computer integration of the Schroedinger equation (with the states expressed in intermediate coupling) resulting from the semi-classical Coulomb excitation theory formulation of the process. Comparison is made with previous results. The associated rate constants at coronal temperatures are given and compared with the corresponding electron impact excitation rate constants. Some cross-section values for the Fe+13 3s23p2P1/2→2P3/2 excitation are also presented.

Electronic excitation of N2and dissociative excitation of O2by proton impact

The technique of energy loss spectroscopy has been applied to a study of inelastic noncharge exchange collisions between protons and molecular nitrogen and oxygen at energies of 0.6–4.0 kev. The most prominent proton impact excitation process in N2 is the Lyman-Birge-Hopfield (LBH) transition (a¹Π g ← X¹Σg+), for which the cross section increases from 0.55 to 3.0 × 10−17 cm² over the observed collision energy range. In O2, dissociation results from excitation into the continuums associated with the upper states of the Schumann-Runge (B³Σu− ← X³Σg−) and Herzberg (A³Σu+ ← X³Σg− or C³Δu ← X³Σg−) transitions. The total cross section for dissociative excitation of O2 increases from 1.0 to 2.6 × 10−17 cm².

Excitation of Helium by Proton Impact

The binary-encounter collision model for ionization of atoms by proton impact proposed by Gerjuoy and Vriens is extended to the problem of proton-impact excitation of a neutral atom from the ground state. We have calculated the proton-excitation cross sections from the ground state of a helium atom to the $n^{1}S$ ($n=2\ensuremath{-}5$), $n^{1}P$ ($n=2\ensuremath{-}5$), and $n^{1}D$ ($n=3,4$) states using a $\ensuremath{\delta}$ function as well as a quantal-momentum distribution function for the target electrons. The calculated cross sections are compared with other theoretical calculations and the measured values.

Proton impact excitation of then1D states of He

The impact parameter version of Born's approximation is used to calculate cross sections for proton impact excitation of the n 1D states of He (n = 3, 4) from 1 1S and 2 1P. The results for 1 1S -> 4 1D are in satisfactory accord with experiment.

Excitation of hydrogen in the impulse approximation

The quantal impulse approximation is applied to the evaluation of electron and proton impact excitation cross sections for atomic hydrogen, a peaking approximation being made in evaluating the matrix elements. It is shown that results previously obtained in the quantal impulse approximation by Akerib and Borowitz are incorrect. The effect of the peaking approximation is to produce very poor results.

The 1 s -2 s excitation of hydrogen atoms by proton impact

It is shown that the cross-sections given by the customary second Born approximation are not reliable because of the neglect of a large term of the fourth order in the interaction energy. The expression for the cross-section obtained by including only terms to the third order in the interaction energy is employed to calculate the cross-sections for the proton impact excitation of the 2 s state of atomic hydrogen, allowance being made for distortion and polarization due to the 1 s , 2 s and 2 p 0.±1 intermediate states. When polarization is ignored by neglecting all terms involving the 2 p states, excellent agreement is found with the distortion approximation calculation of Bates.