Zl. Petrovic et al., ON SPATIAL-DISTRIBUTION OF OPTICAL-EMISSION IN RADIO-FREQUENCY DISCHARGES, Journal of physics. D, Applied physics, 28(11), 1995, pp. 2287-2293
In this paper we present calculations of the spatial distributions of
emission in model argon discharges which correspond to the conditions
of argon discharges in the GEC rf reference cell but are relevant for
other similar rf discharges. The calculations on the basis of the part
icle in cell (PIG) code show that transitions with high threshold ener
gy are predominantly excited by secondary; electrons originating from
the instantaneous cathode while the transitions with lower threshold e
nergy are excited predominantly by electrons accelerated by sheath mot
ion. In addition it is shown that the spatial distribution of 811 nm r
adiation of argon corresponds best to excitation by very low-energy el
ectrons from the metastable state. The different kinetics of excitatio
n of the three groups of transitions mentioned above, in conjunction w
ith different energy dependences of the cross sections and special con
ditions when there is a significant if not dominant contribution of th
e gamma process in sustaining the discharge, give rise to the differen
t spatial distributions of emission which are opposed to the intuitive
ly expected distributions and raise questions about the applications o
f spatial distributions of emission in determining the sheath width an
d in diagnostic techniques such as actinometry.