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MEASUREMENTS OF THE PRODUCTION OF NEON 2p ATOMS BY DISSOCIATIVE
RECOMBINATION
L. Steenhuijsen, N. van Schaik, L.C.A.M. van de Nieuwenhuyzen, F.H.P.
Verspaget
To cite this version:
L. Steenhuijsen, N. van Schaik, L.C.A.M. van de Nieuwenhuyzen, F.H.P. Verspaget. MEASURE- MENTS OF THE PRODUCTION OF NEON 2p ATOMS BY DISSOCIATIVE RECOMBINATION.
Journal de Physique Colloques, 1979, 40 (C7), pp.C7-95-C7-96. �10.1051/jphyscol:1979747�. �jpa-
00219453�
JOURNAL DE PHYSIQUE CoZZoque C7, suppzdment au n07, Tome 40, JuiZZet 1979, pageC7- 95
MEASUREMENTS OF THE PRODUCTION OF NEON 2p ATOMS BY DISSOCIATIVE RECOMBINATION
L.W.G.
Steenhuijsen,N.
Van Schaik,L.C.A.M.
Van de Nieuwenhuyzen,F.H.P.
Verspaget.Eindhoven University of TechnoZogy, Eindhoven, The Nether lands.
Introduction. Determined were in neon the partial recombination coefficients of the 2p levels, the relative population of the 2p levels and the re- combination distribution fractions of the Is levels.
We used neon discharges with d = 31 nm, pressure p = 20, 50, 100 torr and current I = 22 mA. The measurements were carried out in the afterglow of
the discharge I ) . The afterglow radiation can be ascribed to dissociative recombination of molecular ior~s ana electrons;
Ne+ + e
2
(Ne )*: ~e + Ness(ls)+
hv2 2
I n this process highly excited atoms are produced which cascade in a stepwise manner to one of the 2p
levels and from here finally deexcite by radiation to a 1s level. These last transitions cause the ra- diation which we have measured. The recombination coefficient a2 can be splitted in a number of part- ial recombination coefficients a2
,
which each des-i
cribe the recombination yield for each of the various 2p levels. Here we assume that transitions between the 1s levels and levels above 2p are ne- gligible. In the afterglow the various 2p levels are populated in 2 ways: firstly from recombination as described above, secondly from atomic collisional transfer between the 2p levels. These mutual trans- fers prevent the possibility to determine the a
2 i coefficients directly from the spectral distribution of the 1s-2p transitions. We have measured also the eoupling coefficients K. between the 2p levels i
lj
and j. By taking the atomic coupling into account the values of C12i have been determined.
Determination of the partial recombination
coefficient. In the afterglow the electron temperature decreases quickly (at 100 torr in 20 us) to the gas temperature. So the 2p levels are populated only by the process of dissociative recombination. Assuming that the atomic ion density can be neglected, the rate equation for each 2p level can be written as:
j+
ip.(t) is the density of level 2pi at time t in the afterglow; A: is the overall probability of spon-
L
taneous transitions to the 1s levels for level 2pi (A: = $=2Ail, with Ail the spontaneous transition probability from 2pi to Isl); K.. is the'coefficient
1 J
of atomic collisional transfer from level 2pi to level 2p.; n is the ground state atom density.
3 '2
In formula (2) we have neglected the electron coupling between the 2p levels, because of the low electron temperature. For all 2p .levels together we have :
The terms containing the coupling coefficients K.
1 i disappear because the influence of the "intern"
transfers cancel out each other. From (3) follows:
lo
ap.(t) 1 0z
-'--+z ~*~.(t)2 ' = I at .El J J
ne(t) =
'
a2(t) ( 4 )In the remainder of this chapter we will omit the time indication unless it will be necessary. Substi- tution of n2 in (2) and dividing by pi gives:
:Je have measured in the afterglow the tide courses of the relative intensities of the spectral lines originating from each individual 2p -'Is transition
j 1
(j = 1...10, 1 = 2...5). The measured signal I j 1 according to each of these transitions is
8
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1979747
Ijl = njlAjlpj ( 6 )
\,ith q the detection coefficient of the experi- j 1
mental set up, which is dependent on wavelength.
1:eplacing i.1 (5) pj by Ijl/qjlAjl gives:
I alil 10 ''i IAi I.
- --
+ Ai + n Z {K. - K . .I~~ a t s j=l l j J ~ I
J 1 qjlAjlIil
In relation (7) we have determined all quantities which are necessary to calculate QZi. The value of
((111 ).(a1 /at)) follows from our measurements of il il
Iil. However we note that these values are very small
X
compared with the value of A. and so may be neglectei.
In (7) we need the relative values of the detection coefficients qil, which we have calibrated with the use of a tungsten ribbon lamp. From litterature we have taken values for A i 1 ') and a2 4). n g has been calculated for the tubes used. The coupling
3 ) coefficients K i j are measured also
.
We have measured ~1~~ in a 100, 50 a n d 70 !:or]- t v ? c .
However also the disturbing terms of the atomic collisional transfer increase with the gas pressure.
This is disadvantageous because in formula (7) the terms containing K and Kji are rather inaccurate.
i j
For this reason we have determined ~1~~ also at 20 torr where this effect is 5 times smaller. Table 1 gives a survey of the experimental results for a 2i' The inaccuracy is
+
15 %.xith relation (6) we can determine the relative densities of the 2pi levels:
Figure 1 gives the relative densities of the 2p.
levels for pressures of 20, 50 and 100 torr. The inaccuracies are mainly determined by the in- accuracies of the transition probabilities 3).
The recombination distribution fractions give the fraction of the recombination yield produced in the levels ls5, ls4, Isj and Is2 respectively. The fraction fl (1 = 5,4,3,2) can be written as
10 Ijl
C
-
j=1 Qjl
£l= 10 5 I..
C Z
31-
j=l 1=2 r l . . 1 1
The results are given in table 2. They are in good agreement with lit.(5).
References:
1) L.W.G. Steenhuijsen, thesis EUT (1979) 2) L.W.G. Steenhuijsen, ICPIG 14 (1979) 3) S. Inatsugu, Phys.Rev. A11,1,26 (1975) 4) L . Fronunhold, Phys.Rev. 165,44, (1968)
5) L.W.G. Steenhuijsen et al. Proc. ICPIG 13 (1977).
Figure 1:
Measured re Zative
-
d e n s i t i e s of the-
2p Zevet a t 60 ps - i n the aftergzow;rabia I : Vaalues of la2i/a21 a t various pressures
TabZe 2: Recombination d i s t r i b u t i o n fractions for various pressures.
pressures
LO t o r r
I
50 torr 100 torr --.2pl 0.10 0.08 0.07
f 5 4 3
If 2
20 50 100 torr
0.36 0.39 0.42
0.25 0.25 0.25
0. l o 0. l o 0. l o
0.29 0.26 0.23
