described with dynamic equations accounting for both molecular transport and
electron impact excitation/deexcitation.
The cross-sections of vibrational excitation v ! v
0 by electron impact, σ v!v 0 ,
decreases with the increasing difference jv À v
0
j [12, 62, 63] so that in practice,
the main contribution to the population of the vibrational states of H 2 by
electron impact is from excitation to the neighboring vibrational state v ! v Æ 1.
In low temperature, weakly ionized plasma, an important role in the vibrational
kinetics play the so-called vibrational-vibrational (V-V) exchange
(H 2 (v) + H 2 (v
0 ) ! H 2 (v+1) + H 2 (v
0
À1)) and vibrational-translational (V-T) relaxation (H 2 (v) + M ! H 2 (v
0 < v) + M) processes where M is some atom/molecule
(e.g. see [12, 64] and the references therein). Since the Massey parameter (e.g. see
[12]) for the vibrational de-excitation caused by collisions with neutrals in
Fig. 2.7 Experimental
cross-section for the electron
impact vibrational excitation
of molecular hydrogen.
(Reproduced with
permission from [61],
© Elsevier 2002)
0.1
1
10
100
10 –11
10 –10
10 –9
10 –8
10 –7
Power loss rate for excitation [eV cm 3 /s]
H → H(n=2)
H2 → H2(v=1)
T, [eV]
Fig. 2.8 Cooling rate
constants for the excitation
of the first vibrational level
of H 2 and quantum state
n ¼ 2 for atomic hydrogen
as functions of T e
2.4 Application of CRM to Edge Plasma Relevant Species
35