'Polarization-free' measurements are presented of the electron impact excitation of the 1048 Å and 1067 Å resonance lines of argon in the energy range 10–2000 eV. Cross sections are made absolute by normalizing to the optical oscillator strength of the 1048 Å line. Cascade is shown to play a major role in the excitation of the 4s levels. Comparison is made with other experimental results and with theory where available.
Polarization free measurements are presented of the excitation of the 3s3p62S and 3s23p44s2P levels of Ar+ by electron impact. Line intensity measurements yielded relative transition probabilities in good agreement with the recent calculations of Luyken. A double peaked structure is demonstrated to be a common feature of the excitation functions and reasons for this are discussed. Cascade is shown to be an important excitation process for the 4s levels. Comparison is made with other work where available. As a means of calibration of some of the Ar line intensities, a careful measurement was made of the 736 Å Ne excitation function using the Bethe normalization procedure and the known optical oscillator strength.
Polarization-free' measurements are presented of the electron impact excitation of Lyman a by electron impact on H, in the energy range 20-2000 eV. Cross sections are made absolute by normalizing to the data of Mumma and Zipf at 100 eV. A broad maximum in the function occurs around 60 eV, some 20 eV lower than was found by some previous workers. Reasons for this discrepancy are discussed. The high energy behavior of the cross section is analyzed in terms of the Bethe approximation and a value of 0.1 1 is obtained for the square of the dipole matrix element of the transitions involved.
eV.deg) 1/2, FIG. 3. The quantity NE^'^ is plotted as a function of T-E6. N is the index number for the extrema of n(T) (A^ = 0,1, 2, • • • for maxima; i, i, •' • for minima). Open symbols are maxima, closed are minima: circles, 200 eV; triangles, 300 eV; squares, 350 eV.where J LL is the reduced mass and b^ and ^a ^^^ the values of the impact parameter b corresponding to the two scattering potentials for a given scattering angle 0, The linear dependence of NE^^^ on T shows that Ab is approximately independent of r: Afe^0.62a.u. At 350 eV, the behavior of the differential cross section is more complicated: Oscillations appear also in this case, but they seem to be distorted by another phenomenon. In this case the quantity NE^^^ is still a linear function of T-TQ (see Fig. 3), but the slope d(NE^^^)/dT and the values of Ab are slightly larger than for the previous energies. With regard to the diabatic correlation diagram of the Heg"*" system,^ the mechanisms causing the two curve crossings can be considered as possible mechanisms for the He {ls3p, ^P) excitation, corresponding to two electrons being elevated from the (lsag)(2/)au)^^Sg antibonding input channel to {ls(y^)^{4da^)^Z^ and (Isag)-(4^7rg)2 2ng.In an attempt to clarify the parts played by short-range and long-range crossings, we are currently investigating the "companion" level R. L.
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