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Submitted on 1 Jan 1979
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RADIATIVE AND COLLISIONAL DESEXCITATION OF 1P1 AND 3P1 RESONANCE STATES IN XENON.
W. Wieme, M. Vanmarcke, W. Bruynooghe
To cite this version:
W. Wieme, M. Vanmarcke, W. Bruynooghe. RADIATIVE AND COLLISIONAL DESEXCITATION
OF 1P1 AND 3P1 RESONANCE STATES IN XENON.. Journal de Physique Colloques, 1979, 40
(C7), pp.C7-3-C7-4. �10.1051/jphyscol:1979701�. �jpa-00219060�
JOURNAL DE PHYSIQUE CoZZoque C7, suypZ6ment au n07, Tome 40, JuiZZet 1979, page ~ 7 - 3
RADIATIVE AN) COLUSIONAL DESEXCITATION OF 'P, AN) 3 ~ 1 RESONAIKE STATES IN XD(N-
W. Wieme, M. Vanmarcke, W. Bruynooghe.
Laboratoriwn voor Natuurkunde, R i j k s u n i v e r s i t e i t , Rozier 44 Gent, BeZgiwn.
1. Introduction.
In the afterglow of rare gases, the inten- sity of the resonance radiation decays ex- ponentially with time constant 6
I = I e -6t (1
This has been verified by direct observation of the 3 ~ 1 - 1 ~ o radiation in Kr E l ] and Xe 1 2 1 in the pressure range 0,l-20 Torr, and by absorption experiments of the population of the 3 ~ level in Ne, 131 and Ar 1 C41. The decay frequency 6 is given with good accu- recy by the Holstein imprisonment theory, and in cylindrical geometry we find
Here R is the cylinder radius, 1 the wave- length of the resonance line and T~ the na- tural lifetime of an atom in the resonance state. In this paper we present an absorp- tion measurement on the 3 ~ level and emis- 1
sion measurements of the 3 ~ 1 - ' ~ o and 'P,- 'So resonance radiation in Xe. It will be shown that at higher pressures collisional destruction processes become important.
The detector is a EMI-GENCOM 6-263315. The PM signal is analysed with a DATALAB DL 920
transient recorder with a time resolution of 50 ns.
3. Results.
a) Absorption
For the absorption measurement the wave- lengths 492,3 nm and 491,7 nm corresponding to the transitions 6s4-7pg and 68,-6p, were chosen, these being the most intense in the visible region. Assuming an exponeqtial de- cay, the lifetime Ts of the imprisonned re- sonance state is given by In In I / I = - t / ~ +
S
constant where I. represents the intensity before and I the intensity after absorption.
In the case of weak absorption (Io-I<<Io)
this becomes t
ln(Io-I) =
- -
+ constant.s The results are given in Fig.1.
The decay constant 6 is seen to be reasona- bly constant in the pressure range 0,01-10 Torr. At higher pressures some pressure de- pendence is observed, but these points are not taken into account for the analysis.
2. Method.
The experimental set-up for the absorption experiment is simi,lar to the one used in[5]
except for the detection system which con- sist' of a 1P21 photomultiplier followed by a PAR TDH-9 Waveform Eductor which allows the afterglow to be recorded in 100 chan- nels. For the direct measurement of the re- sonance radiation the discharge tube was provided with a LiF window. The wavelength was selected with a McPherson 218 VUV mono- chromator with a 2400 l/mm grating blazed at 150 nm. Depending upon intensity, a re- solution of 0.05 up to 0,5 nm was used.
This was sufficient to discriminate against the well-known VUV continuum radiation of the rare gases.
This pressure dependence is discussed in the next paragraph. The imprisonment time is found to be : 'rs = 7,6+0,8 us, and, with
(2) this leads to a natural lifetime T~ = 4,3 k 0,5 ns
or, using the relation
m c gi X 2
fTN =
- -
8a2e2 gk ( 3 ) we find an oscillator strength for the
3 p 1 - 1 ~ o transition : f = 0,226
+
0,025These values are in good agreement with li- terature [ 2 1 . The lifetime of the ' P ~ re- sonance state could not be measured in ab- sorption due to the low concentration of 'P, atoms.
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1979701
by Emission
-
147 nm dmission, or 3 ~ 1 - 1 ~ o transition.The decay consksts of two components and is fitted with a computer to a curve :
f P A e-dft + B (4) Here df represents the time constant of a few us, while ds is a much slower decay, at lesst for pressures up to about 20 Torr. It can easily be demonstrated (see also ref 161) that in Xe for pressures lower than 60 Torr we have within a 5 % accuracy :
df = 6 + aRM + aRS
aRM represents the reaction rate constant due to collision-induced transitions from the resonance level R(~P,) to the nearby metas table level M('P,), while aRS indica- tes the formation of excimer states S through collisions of resanance states R with ground state atoms.
The measured fait decay df is given in Fig.2 for pressures between 0,02 and 70 Torr. The points are least-square fitted to give a curve : df = 1,28.105+3330p + 27p2 6 = 1.28.1 corresponds td T = 798
in agreement with the absorption experiment.
3800 p represents collisonal desexcitation of atoms to the 3 ~ metastable level. 2
From detailed balancing considerations we find the collisional excitation of x ~ ( ~ P ~ ) to x ~ ( ~ P ~ ) to be 18 p. The collisional de- cay of 3 ~ 2atoms Was found to be 113p+87p2 C51. It follows that the collision induced emission of x~(~P,) proceeds with a rate 95 p. The term 27 p2 represents excimer formation in three-body collisions. The re- sulting excimer can be either the o:, or the l a 3 z + states. Two-body and three-body
g
rate constants are summarized in Table 1 and compared with literature.
-
129,6 nm emission, ' P ~ - ' S ~ transition.This line has viry low intensity and is fitted like (4). The slow component has not been identified. The fast component can be fitted to a curve :
vf=
1 , 2 9 1 0 ~ + 1 , 9 4 1 0 ~ p At pressures above 0,8 Torr, this decay is too dependent on discharge pulse current to be taken into account. (Fig.3).With B = 1,29 10' we find for 'P, : T* = 4,lf0,6 ns ; f = 0,181+0,036 The collisional deiexcitation proceeds to either the lower levels, or the nearby 3 ~ 1 .
References.
Reaction Rate constant
R.Turner,Phys.Rev.l58,121,1967.
W.Wieme,P.Mortier,Physica 65,198,1973.
A.V.Phelps,Phys.Rev.,114,1011,1959.
E.Ellis,N.D.Twiddy,J.Phys.B,2,1366,1969.
W.Wieme,J.Phys.B,4,850,1974.
W.Wieme,J.Lenaerts : submitted for this conference.
P.K.Leichner et al,,Phys.Rev.13,1787,76.
R.Brodmann,G.Zimmerer,J.Phys.B,10,3395, 1977.
N.Sadeghi,J.Sabbagh,Phys.Rev.l6,2336,77.
This work 3 ~ 1 +
'so+
3 ~ 2 + 1 ~ 0 3330 3 ~ 2 + SO+ 3 ~ 1 + 1 ~ 0 18 13 ~ 2 + 1 ~ 0 + 2 1 ~ O + h ~ 95 3 ~ 1 + 2 1 ~ o + ~ e 2 + 1 ~ o 2 7 'PI+
1s0+3s,+1s0
19.10~pig. 1
y i H z l ' " I ' ' " I ' l r 1 8
5 1 8 -
L -
Literature 9100 [71
49 [71 71 C71
ctg [a;
21.10 [9]
)
