Excitation of the 2p[sub 9] state of rare gases by electron impact.

Emission cross sections for the np → ns transition (Ne: n=3, Ar: n=4, Kr: n=5) have been systematically studied. The 2pg → 1s[sub 5] transition in Paschen's notation is of particular interest because the 2p[sub 9] state is a pure triplet state and well represented by ³D[sub 3] in the LS-scheme. Theoretical excitation cross sections of the 2p[sub 9] state show almost ∼E[sup -3] dependence on electron energy E, whereas, experimentally obtained results descend more slowly. A time resolved lineintensity measurement was carried out in order to clarify the discrepancy and to have more insight into the excitation mechanism of the 2p[sub 9] state. It was found that a considerable part of the population of the 2p[sub 9] state is due to the cascade transitions from the higher lying Rydberg states and that the descent of the level excitation cross section of the 2p[sub 9] state at high energies is slower than expected by the DWA theories. [ABSTRACT FROM AUTHOR]