Primer on Collisions
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II) Electron-Impact Excitation out of the ground state of Atoms

C. Excitation of Neon, Argon

Neon 2p53p levels


So far, we have only considered the shape of the excitation functions. Let us now examine the magnitudes of the cross sections. The following table lists the cross section at 100 eV for the ten 2p (Pachen notation) of neon in units of 10-20 cm2.
LevelsJQ(100 eV)          LevelsJQ(100 eV)
2p1 0160    2p2 123
2p3 015    2p5 116
2p4 264    2p7 124
2p6 261    2p10 117
2p8 241    2p9 318
Note the general trend that the cross sections for excitation into levels with even J are larger than cross sections into odd J levels (but not quite as convincing as with argon). Let us see how this trend can be explained using the same multi-pole field expansion as with helium.


This is the same as a one electron excitation 2p (l=1)-->3p (l'=1). From the mulipole field analysis (k=0,1,2,3,...) we find that for l=1-->l'=1, only terms with k=0 and k=2 are compatible. Thus,
Ne( 2p6, J=0) --> Ne( 2p53p, J'=0 or 2)    allowed
Ne( 2p6, J=0) --> Ne( 2p53p, J'=1 or 3)    forbidden in 1st approximation

Thus, our standard multipole expansion arguement agrees with the experimental data:

Q( 2p54p, even J ) » Q( 2p53p, odd J)

references:
Experimental and Theoretical Studies of Electron-Impact Excitation of Neon Francis A. Sharpton, Robert M St. John, Chun C. Lin, and Fredric E. Fajen, Physical Review A 2 (1970) 1305-1322.
last updated: May-15-1997