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A Caltech Library Repository Feedhttp://www.rssboard.org/rss-specificationpython-feedgenenFri, 12 Apr 2024 00:09:11 +0000Differences in the Angular Dependencies of Spin- and Symmetry-Forbidden Excitation Cross Sections by Low-Energy Electron Impact Spectroscopy
https://resolver.caltech.edu/CaltechAUTHORS:RICjcp68
Authors: {'items': [{'id': 'Rice-J-K', 'name': {'family': 'Rice', 'given': 'J. K.'}}, {'id': 'Kuppermann-A', 'name': {'family': 'Kuppermann', 'given': 'Aron'}}, {'id': 'Trajmar-S', 'name': {'family': 'Trajmar', 'given': 'Sandor'}}]}
Year: 1968
DOI: 10.1063/1.1668744
Optically forbidden electronic transitions can be produced by low-energy electron impact. Recent experimental investigations of helium (1-3) have shown that the differential scattering cross sections for forbidden excitations are generally enhanced relative to those for allowed ones at low incident energies and large scattering angles.
We have now observed marked differences in the angular and energy dependencies of differential cross sections for various kinds of forbidden (spin, symmetry, or both) transitions in helium at low incident energies. Such differences may well provide a basis for determining the nature of optically forbidden transitions detected by electron-impact spectroscopy in other atoms and molecules.https://authors.library.caltech.edu/records/3m81n-gyb84Angular Dependence of Low-Energy Electron-Impact Excitation Cross Section of the Lowest Triplet States of H2
https://resolver.caltech.edu/CaltechAUTHORS:TRAjcp68
Authors: {'items': [{'id': 'Trajmar-S', 'name': {'family': 'Trajmar', 'given': 'S.'}}, {'id': 'Cartwright-D-C', 'name': {'family': 'Cartwright', 'given': 'D. C.'}}, {'id': 'Rice-J-K', 'name': {'family': 'Rice', 'given': 'J. K.'}}, {'id': 'Brinkmann-R-T', 'name': {'family': 'Brinkmann', 'given': 'R. T.'}}, {'id': 'Kuppermann-A', 'name': {'family': 'Kuppermann', 'given': 'A.'}}]}
Year: 1968
DOI: 10.1063/1.1670073
The differential cross sections for the electron-impact excitation of the lowest triplet states of molecular hydrogen (b3Sigmau+,a3Sigmag+) have been calculated from threshold to 85 eV impact energy using the Ochkur–Rudge theory. For the X1Sigmag+ --> b3Sigmau+ transition, the relative differential cross sections were measured with a low-energy, high-resolution electron-impact spectrometer from 10° to 80° scattering angle and impact energies of 25, 35, 40, 50, and 60 eV. Theory and experiment are in good agreement for the shape of the differential cross section for energies of 35 eV and above. However, at 25 eV, the theory continues to predict a rather well-developed maximum in the cross section at around 40° while the experimental cross sections are more isotropic. An appreciable contribution to the inelastic scattering in the energy loss region from 11 to 14 eV due to excitation to the a3Sigmag+ and/or c3Piu states is definitely established from the observed angular distributions. A quantitative evaluation of the individual angular behavior of the excitations in this region, however, would require a resolution higher than the presently available one of 0.030 eV.https://authors.library.caltech.edu/records/5w02x-hbm98Differential and integral cross sections for excitation of the 2(1)P state of helium by electron impact
https://resolver.caltech.edu/CaltechAUTHORS:TRUpra70
Authors: {'items': [{'id': 'Truhlar-D-G', 'name': {'family': 'Truhlar', 'given': 'Donald G.'}}, {'id': 'Rice-J-K', 'name': {'family': 'Rice', 'given': 'James K.'}}, {'id': 'Kuppermann-A', 'name': {'family': 'Kuppermann', 'given': 'Aron'}}, {'id': 'Trajmar-S', 'name': {'family': 'Trajmar', 'given': 'S.'}}, {'id': 'Cartwright-D-C', 'name': {'family': 'Cartwright', 'given': 'D. C.'}}]}
Year: 1970
DOI: 10.1103/PhysRevA.1.778
Differential scattering cross sections for excitation of helium by electron impact from its ground state to its 21P excited state have been measured at four incident electron energies in the range 26-55.5 eV for scattering angles between 10° and 70°, and at 81.6 eV for scattering angles between 10° and 80°. These differential cross sections have been placed on an absolute scale by normalizing them to the experimental absolute integral cross sections of Jobe and St. John. These experimental differential and integral cross sections have been compared with the results predicted by the Born approximation, and by several other first-order approximations in which direct excitation is calculated in the Born approximation and exchange scattering by various Ochkurlike approximations. The calculations provide reliable tests of these scattering theories since they are made using the accurate generalized oscillator strengths of Kim and Inokuti. As expected, these first-order theories are poor near threshold and exchange is important at high scattering angles for all energies. Further, the absolute magnitude of the calculated integral and small-angle differential cross sections is too large and is within 50% of experiment only at energies greater than 80 eV. These first-order models are in qualitative agreement with the experimental angular dependence at 34-81.6 eV for scattering angles between 10° and 40°. At higher scattering angles (corresponding to momentum transfers greater than about 1.6 a.u.), the calculated differential cross sections fall well below the experimental ones. The phase between the direct and exchange scattering amplitudes was found to be important at all energies, and is apparently not predicted correctly by any of the first-order models examined here. Some approximations for the exchange (e.g., Ochkur approximation and the post interaction form of the Ochkur-Rudge approximation) were found to be better for integral cross sections and some (e.g., prior Ochkur-Rudge approximation) were better for differential cross sections. The use of good analytic self-consistent-field (SCF) wave functions for both the ground and excited states was tested by computing generalized oscillator strengths from them and comparing these results with the calculations using the accurate generalized oscillator strengths. The SCF functions yield differential cross sections in quantitative disagreement (20%) with the accurate results, although the energy and angle dependence of the cross sections is predicted qualitatively correctly.https://authors.library.caltech.edu/records/32pg8-s9p48Electron scattering by H2 with and without vibrational excitation. III. Experimental and theoretical study of inelastic scattering
https://resolver.caltech.edu/CaltechAUTHORS:TRAjcp70
Authors: {'items': [{'id': 'Trajmar-S', 'name': {'family': 'Trajmar', 'given': 'S.'}}, {'id': 'Truhlar-D-G', 'name': {'family': 'Truhlar', 'given': 'D. G.'}}, {'id': 'Rice-J-K', 'name': {'family': 'Rice', 'given': 'J. K.'}}, {'id': 'Kuppermann-A', 'name': {'family': 'Kuppermann', 'given': 'A.'}}]}
Year: 1970
DOI: 10.1063/1.1673679
The ratios of the differential cross sections (DCS's) for excitation of the first, second, and third vibrational states of H2 in its ground electronic state to the elastic DCS have been measured as a function of scattering angle in the 10°–80° range and impact energy in the 7–81.6-eV range. From these ratios the DCS's corresponding to transitions from the ground to the first two vibrationally excited levels (fundamental and first overtone bands) were obtained by utilizing the elastic cross sections determined in the previous paper (II). In addition, the DCS for excitation of the second overtone band was determined for an impact energy of 10 eV. By angular extrapolation and integration of the DCS's the integral cross sections for the vibrational excitations were also determined. In addition, all these cross sections have been calculated using a quantum-mechanical method based on potential scattering in a plane wave scattering approximation which is described in Part I of this series. The present experimental and theoretical cross sections and previous measurements and calculations are compared. The calculated DCS ratios and the DCS's themselves for the fundamental excitation are in good agreement with experiment at 7 and 10 eV; however, at higher energies the calculated DCS's are generally larger than the experimental ones, at some angles by as much as a factor of 10. The calculated ratio of the DCS for the fundamental excitation to the elastic DCS shows a minimum as a function of angle, in qualitative agreement with the experimental results in the 13.6–81.6-eV energy range. The experimental DCS's for vibrational excitation also show a deep minimum. For excitation of the first overtone vibration, the experimental ratios are an order of magnitude larger than the calculated ones at low energy but in better agreement for the magnitude at higher energy. This discrepancy at low energies is explained in terms of resonance scattering. Our experiments are in good agreement with those of others in the few (low energy) cases where comparison is possible.https://authors.library.caltech.edu/records/vc4qr-4fe32