Cross Sections For Simultaneous Excitation Research Articles

Simultaneous excitation and ionisation of helium by fast projectiles

The cross sections for simultaneous excitation and ionisation in helium following impact of fast electrons, protons and Cq+ (q=3-6) ions have been investigated by measuring the vacuum-ultraviolet radiation from transitions in HE II (np-1s) in the wavelength region 220-315 AA. The cross sections obtained with 500-2000 eV electrons are found to be larger by a factor of 1.4-2.3 than those obtained with protons of the same velocity (0.92-3.76 MeV). The difference is discussed in terms of an interference between two excitation-ionisation mechanisms.

Simultaneous electron-photon excitation of hydrogen and helium

Total and differential cross sections for simultaneous excitation of H(2s), H(3s) and He(1s 2s) by electron impact in the presence of a photon field have been calculated in second-order perturbation theory. The characteristics of the results are interpreted in terms of their physical origin. The off-shell excitation cross section for the He(1s 2s) state is found to be one order of magnitude smaller than that for excitation of the H(2s) state. This is consistent with our expection that atoms with higher dipole-polarisability should favour larger off-shell cross sections for transitions betweens-states.

Simultaneous excitation of both collision partners in He-He collisions

The energy dependence of the cross section for simultaneous excitation of both collision partners to the 33D state in He-He collisions has been measured at incident energies between 0.9 and 3.5 keV. At an incident energy of 1750 eV this cross section reaches a maximum of about 5.5% of the cross section for excitation of one atom to the 33D state, whatever the final state of the other atom. Further, at 1500 eV ratios have been measured of the cross sections for simultaneous excitation of one atom to the 33D state and the other to different n>or=3 triplet states. From these measurements it can be concluded that the 33D state is only for about 7% simultaneously excited with n>or=3 triplet states, which means that in simultaneous excitation with one atom in the 33D state there is a more than 90% probability to find the other atom in the 23S or 23P state.

Determination of the electron temperature of the tenuous pulsed argon ion laser plasma by means of the line intensity ratio technique

The validity of the diagnostic line-intensity ratio method for determination of the electron temperature was examined for a tenuous, NLTE pulsed argon ion laser plasma. Recently measured cross sections for simultaneous excitation and ionization of the upper levels of the argon ion laser were used and averaged over the velocity distribution, assumed Maxwellian. The electron temperature was determined by observing the sidelight intensity ratio of doublet 4765 A and quartet 4806 A transitions, and it was found to be 1.65 eV. This result is in agreement with electron temperature values obtained by the time resolved measurement and the double probe method, respectively. The theory of the positive column, where wall effects are not considered, gives somewhat larger values as an upper bound.