Relative Differential Cross Sections Research Articles

Electron impact ionisation of argon at intermediate energy and momentum transfer: an (e,2e) investigation

Relative differential cross sections for the coplanar asymmetric (e,2e) reaction in argon have been measured at 1 keV incident energy in three different kinematics. Depending on the scattering angle, theta a, the chosen kinematics select either ionising collisions belonging to the Bethe ridge ( theta a=20 degrees ) or processes in the intermediate region between the pure dipolar and binary regimes. Experiments are compared with the theoretical predictions of plane-wave, eikonal-wave and distorted-wave impulse approximations. The results show that, independently of the symmetry of the ionised orbital and even at iron recoil momentum as large as 2.6 au, the distorted-wave impulse approximation (DWIA) satisfactorily describes the triple differential cross section, whenever the kinematics complies with the Bethe ridge conditions. Off the Bethe ridge, factorisation of the DWIA cross section into a two-electron collision amplitude times a structural form factor can be a bad approximation.

Ionisation of atomic hydrogen at intermediate momentum transfer

Relative differential cross sections for the asymmetric coplanar (e, 2e) reaction have been measured in three energy-sharing regions, for two of which the ionisation peak is about 1 au off the Bethe ridge. Momentum transfer is intermediate between large (binary) and small (dipole) values, where the distorted-wave impulse and second Born approximations respectively give a good account of the experimental data. In addition to these approximations the distorted-wave Born approximation is calculated. It is somewhat superior to the distorted-wave impulse approximation and very much better then the second Born approximation.

Effects of vacuum polarization in hadron-hadron scattering.

To investigate the effect of vacuum polarization in the Coulomb interaction between hadrons, the relative differential cross section for elastic /sup 12/C-/sup 12/C scattering at E/sub lab/ = 4 MeV has been measured with high precision. The data are compared to theoretical calculations that take into account the contribution of the U-dieresishling potential and other small contributions. Data and calculation agree within 1.5 standard deviations. This constitutes a test of the vacuum polarization on the 7% level.

Generalized oscillator strength for the 3p6-->3p5(4s,4s') transitions in argon.

Absolute values for the generalized oscillator strength (GOS) for the 3${p}^{6}$\ensuremath{\rightarrow}3${p}^{5}$(4s,4s') transitions in argon ${(}^{1}$${\mathrm{S}}_{0}$) have been determined by 1-keV electron scattering. The relative differential cross section, measured in the angular range of 1.0\ifmmode^\circ\else\textdegree\fi{}--15\ifmmode^\circ\else\textdegree\fi{}, has been made absolute by comparison with known absolute values for the elastic differential cross section, and the results converted to GOS. The GOS's have also been calculated, using both the first Born and Glauber approximations, and the results are compared to the experimental values.

An angle-resolved mass-spectrometric study of non-dissociating excited states of CS +2 formed in 5 keV collisions of CS +2 with rare-gas targets

High-resolution energy-loss spectra were obtained for 5 keV CS + 2 ions scattered through selected angles within the range 0–0.52° following collisions with rare-gas target atoms. Excitation to CS + 2 ( A ) and CS + 2 ( B ) electronic states was clearly observed for all of the five targets used and relative differential cross-sections constructed for each process. From these, integrated cross-sections and most-probable centre-of-mass frame scatter angles, Θ c, were determined. The former increase across the series He to Xe whilst the latter decrease, both trends suggesting that collisions occur with increasingly larger values of impact parameter across this series. The most-probable scatter angles, θ c, in the laboratory frame were largest for a neon target and least for helium and also increase with increasing endothermicity of reaction. If such values (typically 0.1–0.3°) represent lower limits for the θ c values associated with excitation to dissociating states of CS + 2, then collisional scattering will not be negligible in relation to fragmentation scattering in CID experiments involving this molecular ion.

ChemInform Abstract: Electron‐Impact Spectroscopy of Acetaldehyde.

Acetaldehyde has been studied by the technique of low‐energy variable‐angle electron energy‐loss spectroscopy. With this method the low‐lying spin‐forbidden transitions have been located via the behavior of the relative differential cross sections, providing the first identification by this technique of such states in acetaldehyde. High‐lying states were also investigated and some assignments of dipole symmetry‐forbidden/quadrupole symmetry‐allowed excitations were made on the basis of characteristic angular behavior, evident for the asymmetric molecule acetaldehyde just as for the symmetric molecules formaldehyde and acetone. Through a comparison of the acetaldehyde results with those for formaldehyde and acetone the trends in the allowed and forbidden transition energies were examined as a function of methyl substitution and found to be relatively linear.

Large-angle keV-energy He-He scattering measurements with use of a correlated two-particle coincidence detector.

Relative differential cross sections for He-He collisions in the keV-energy range are reported for laboratory scattering angles between 35\ifmmode^\circ\else\textdegree\fi{} and 56\ifmmode^\circ\else\textdegree\fi{}. The experiment utilizes two position-sensitive detectors to detect both collision products in coincidence following the collision. A strong periodic variation in the differential cross section with scattering angle is present whenever the collision partners have identical nuclei and is ascribable to well-known interference effects resulting from the indistinguishability of the collision products. Calculations of these differential cross sections considering only the Coulomb interaction between nuclei of the colliding atoms agree well with the experimental data.

The neutron-proton scattering length in the reaction9Be(p, np)8Be at 7.5 MeV

The relative differential cross section of the9Be(p, np)8Begs reaction at 7.5 MeV has been measured in an FSI geometry. A strongn-p FSI peak was observed with virtually no sequential decay modes interfering. The Watson-Migdal analysis of this peak yields the scattering lengthanp=−23.8−1.2−1.1 fm with the effective rangernp=2.76 fm.

Crossed-beam investigation of the single-electron charge transfer process Kr 2+ + He → Kr + + He + at sub-eV collision energies

The elementary single-electron charge transfer reaction between Kr 2+ and He has been investigated in a scattering experiment at the collision energies 0.3–0.5 eV. Relative differential and total cross-sections of the main state-to-state processes have been obtained. The spin-orbit states of Kr +, 2 P 3/2 and 2 P 1/2, are populated about equally in collisions between Kr 2+ ( 1 S 0) and He; the ratio of the cross-sections Kr 2+ ( 1 D 2) → Kr + ( 2 P 3/2) to Kr 2+ ( 1 S 0) → Kr + ( 2 P J ) is approximately 10 −2.

Electron-impact spectroscopy of acetaldehyde

Acetaldehyde has been studied by the technique of low-energy variable-angle electron energy-loss spectroscopy. With this method the low-lying spin-forbidden transitions have been located via the behavior of the relative differential cross sections, providing the first identification by this technique of such states in acetaldehyde. High-lying states were also investigated and some assignments of dipole symmetry-forbidden/quadrupole symmetry-allowed excitations were made on the basis of characteristic angular behavior, evident for the asymmetric molecule acetaldehyde just as for the symmetric molecules formaldehyde and acetone. Through a comparison of the acetaldehyde results with those for formaldehyde and acetone the trends in the allowed and forbidden transition energies were examined as a function of methyl substitution and found to be relatively linear.

Dynamics of H+ + Kr and H+ + Xe elastic and charge-transfer collisions: State-selected differential cross sections at low collision energies.

Elastic and charge-transfer scattering of protons by Kr and Xe targets has been investigated in a crossed-beam experiment at collision energies ${E}_{\mathrm{c}.\mathrm{m}.=30.6}$ and 51.7 eV. The charge-transfer collisions led to the formation of ${\mathrm{Kr}}^{+}$(${\mathrm{}}^{2}$${\mathrm{P}}_{3/2}$,${\mathrm{}}^{2}$${\mathrm{P}}_{1/2}$)+H(n=1) and ${\mathrm{Xe}}^{+}$(${\mathrm{}}^{2}$${\mathrm{P}}_{3/2}$,${\mathrm{}}^{2}$${\mathrm{P}}_{1/2}$)+H(n=1,n=2) products respectively. Interference patterns in the state-selected relative differential cross sections were clearly resolved and have been ascribed to primary and secondary rainbows and/or Stueckelberg-type oscillations. The ${\mathrm{H}}^{+}$+Xe collisions have also been investigated theoretically by the exact close-coupling method. A good agreement between theory and experiment has been found. A novel method for determining the absolute H-atom detection efficiency is suggested.

Elastic scattering of intermediate-energy electrons by sodium, potassium and rubidium atoms

Relative differential cross sections are presented for elastic scattering of electrons by sodium, potassium and rubidium atoms in the energy range from 150 to 500 eV. The data were obtained at angular intervals of 10 degrees from 30 degrees to 120 degrees . The cross section curves show a minimum around 100 degrees for sodium and potassium and 80 degrees for rubidium, the depth of the minimum decreasing with increasing energy. A comparison with previous experimental data and various theoretical models indicates the dominance of static and absorption potentials in the elastic scattering channel and the weak binding of valence electrons in the alkali atoms.

An electron-impact spectroscopy investigation of CH3 and some of its pyrolytic precursors

The electronic spectrum of the methyl radical CH3 was investigated by the technique of variable-angle electron energy-loss spectroscopy. By means of pyrolytic decomposition three possible sources of this radical were tried (tetramethyl tin, ethyl nitrite, and di-t-butyl-peroxide). The spectra of these precursors were obtained. Using di-t-butyl-peroxide, relative differential cross sections for the lowest allowed A″2 3s Rydberg transition in CH3 (5.73 eV) were determined at incident energies of 50 and 25 eV. The behavior of the differential cross section for this band is analogous to that of a spin-allowed transition in a closed shell system and, as expected, in the vicinity of this band no transition of a spin-forbidden nature is detected.

Tensor-force effects in the 2H(d

Vector analyzing powers, tensor analyzing powers, and relative differential cross sections have been measured for the $^{2}(\mathrm{d}\ensuremath{\rightarrow}$,\ensuremath{\gamma}${)\mathrm{}}^{4}$He reaction at an incident energy of 10 MeV. Multipole decomposition and partial-wave analysis reveal that about 15% of the cross section involves processes in which the tensor force plays a role, either in the entrance or exit channel. Contrary to earlier claims, the reaction cannot be used to determine the D-state admixture in the $^{4}\mathrm{He}$ wave function unless the D state of the deuteron and other tensor-force effects in the entrance channel are taken into account.

Positron differential elastic-scattering cross-section measurements for argon.

Relative elastic differential cross sections are measured for 100- to 300-eV positrons and electrons scattering at 30/sup 0/ to 135/sup 0/ angles from argon atoms in the first crossed-beam experiment to be performed with a positron beam. Good agreement is found with prior electron work and the few available calculations for positrons. The shapes of the positron and electron differential cross-section curves at 100 eV are quite different, but appear to become more similar at 300 eV.

Electronic and vibrational excitation in K-N2 collisions

The dynamics of alkali atom/nitrogen molecule collisions have been probed by the measurement of relative differential cross sections for a range of electronic and vibrational exit channels. The measurements were made over a range of collision energy from 40 to 110eV c.m. and cover reduced scattering angles from 30–400 eV°, all the measurements being made in the small angle regime. The observations are interpreted on the basis of a simple model and are shown to be compatible with the existence of a substantially ionic doorway state in the collision.

Relative differential cross section for the excitation of the 3 (1)P (ml=0) state of helium.

The differential cross section of the 3 ${\mathrm{}}^{1}$P (${m}_{l}$=0) state in helium is investigated for scattering angles up to 50\ifmmode^\circ\else\textdegree\fi{} for electrons with an incident energy of 70 eV. This is done by detecting the inelastically scattered electrons in coincidence with the 501.6-nm photons that are emitted when this state decays to the 2 ${\mathrm{}}^{1}$S state. The photon detector has a nonpolarizing filter and is located in the scattering plane at right angles to the incident beam. For this geometry, the data will yield a relative differential cross section for the 3 ${\mathrm{}}^{1}$P (${m}_{l}$=0) state. The results are compared with several theories. It is found that the present results agree best with the excited-state model of a distorted-wave Born approximation by Madison.

Absolute experimental differential and integral electron excitation cross sections for atomic oxygen: 1. The (³P → ³So) Transition (1304 Å) at 100 eV

The absolute differential electron scattering cross section for the atomic oxygen (³P → ³So) transition (1304 Å) has been measured at 100‐eV electron impact energy. The experimental apparatus was a variable angle and incident energy electron spectrometer coupled to a microwave discharge free supersonic jet expansion source. The source produced an intense jet containing O2, H, O, and He with an O/O2 ratio typically greater than 2.5. Relative densities of species in the jet were determined from the zero angle forward electron energy loss spectrum and the known optical oscillator strengths for transitions in each species. Measured relative differential cross sections (DCS) were put on an absolute scale by comparison with the known DCS for the He 2 ¹P transition. As a check on the atomic oxygen values a simultaneous determination was made of the DCS for the H (1s) → H (n = 2) transition. Results for this transition were in excellent agreement with previous experimental and theoretical results. An additional check on the DCS values for O and H was given by the extrapolation within experimental error of the generalized oscillator strengths calculated from the measured DCS values to the optical oscillator strengths at zero momentum change. The O ³So DCS is extremely forward peaked and decreases by almost 5 orders of magnitude from 0° to 90° scattering angle. The integral, direct excitation, cascade‐free cross section at 100 eV is 6.4 (±1.0) × 10−18 cm².

Differential electron scattering cross sections for the 3 (2)S to 3 (2)P0 h, K transitions in MG II - Comparison of experiment and theory

Angular differential electron scattering cross sections are reported for the unresolved inelastic 3s (2)S to 3p (2)P0 h, k transitions in Mg II for the first time. Relative differential cross sections have been measured at 35 eV and 50 eV in the angular range of Theta between 6 and 17 deg using the newly developed electron energy loss technique in a crossed electron-ion beam geometry. Theoretical values have been calculated in a five-state close-coupling approximation in which 3s, 3p, 3d, 4s, and 4p states were included, and to which measurements were normalized at Theta = 12 deg.

Excitation of vibrational levels up to ν=17 in N2by electron impact in the 0-5 eV region

The energy dependences of the vibrational excitation of up to nu =17 by electron impact in N2 are reported from threshold to approximately 5 eV. The resulting relative differential cross sections are normalised to the absolute integral value of Jung et al. (1982) at 2.25 eV. The curve shapes are compared with published theoretical results where available. The direct process near threshold of the first three vibrational levels is also investigated and the nu =1 results are compared with the results of electron drift experiments.