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Published December 15, 1968 | public
Journal Article Open

Angular Dependence of Low-Energy Electron-Impact Excitation Cross Section of the Lowest Triplet States of H2


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.

Additional Information

©1968 American Institute of Physics. Received 12 July 1968. The authors are grateful to Dr. J.A. Simpson and Dr. C.E. Kuyatt for valuable advice concerning the design of the instrument and to Mr. G. Steffensen for his help in carrying out the measurements. They would also like to acknowledge helpful discussions with Professor R.M. Pitzer and Professor W.A. Goddard, and Mr. D.G. Truhlar of the California Institute of Technology, concerning certain aspects of the theoretical work. Work supported in part by the National Aeronautics and Space Administration, Contract NAS7-100. Albert Amos Noyes Laboratory of Chemical Physics, Contribution No. 3705. Work supported in part by the U.S. Atomic Energy Commission. Report Code CALT 532-33. Erratum: Angular Dependence of Low-Energy Electron-Impact Excitation Cross Section of the Lowest Triplet States of H2 S. Trajmar et al. J. Chem. Phys. 51, 3152 (1969).


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