CC BY
46
УДК 661.939-128+539.19
Вестник СПбГУ. Сер. 4. 2013. Вып. 4
V. A. Ivanov, A. S. Petrovskaya, Yu. E. Skoblo
DISSOCIATIVE RECOMBINATION OF HETERONUCLEAR HeNe+ IONS WITH ELECTRONS INTO 5s AND 4d LEVELS OF THE NEON ATOM*
The aim of this work is the measurement of partial dissociative recombination rate of HeNe+ ions with electrons into 5s (3sj in Pashen's notation) excited levels of neon atom in He-Ne afterglow plasma by means of spectroscopic method. Plasma was produced in a glass tube by a pulsed (128 ^s) discharge with a long (8.3 ms) afterglow. The densities of particles are: [He] = 1.2 • 1018, [Ne] = 1013 cm-3, the electron density about ne = 1011 cm-3. A more detailed description of the experimental setup is presented in [1, 2]. In our previous paper [3] we established that the main processes of the formation of the 3sj excited states of the neon atom are the following:
1. the energy transfer process
He(2%) +Ne ^ Ne(2p55s) + He(1%); (1)
2. the dissociative recombination of the HeNe+ ions with electrons
HeNe+ + e ——-► Ne(2p55s, 3Si) + He. (2)
The energy transfer (1) is the main process which populates the 3s j state of the neon atom in discharge and in the early afterglow. In the late (t > 200 ^s) afterglow the population of the 3sj states is due to the recombination of electrons with HeNe+ ions (2) when the gas and electron temperatures are equal.
The method of measurement of the partial recombination rate coefficient a3s _ is based on the measurement and comparison of relative values of the spectral line intensities of the neon atom. Measured in the experiment were the time dependences of the spectral line intensities of the neon atom emitted from the radiation transitions: 2p_p ^ 1sj and 3sj ^ 2pk. In order to calculate the values of the recombination rate agseNe the relative values of the spectral line intensities were studied in the afterglow of the He-Ne plasma. The same method for the calculation of the partial recombination rate coefficient was applied in paper [4].
The line intensities were measured by the multichannel photon counting method and the value of the line intensities can be expresed by the following equation:
N\j = GK^S (\j )r,
Vladimir Aleksandrovich Ivanov — Profesor, Saint Petersburg State University; e-mail: ivanov19473@yandex.ru
Anna Stanislavovna Petrovskaya — Post-graduate student, Saint Petersburg State University; e-mail: anita3425@yandex.ru
Yuri Eduardovich Skoblo — Associate Profesor, Saint Petersburg State University; e-mail: yuri_skoblo@mail.ru
* По материалам международного семинара «Collisional processes in plasmas and gas laser media», 22—24 апреля 2013 г., физический факультет СПбГУ.
Семинар был проведён при софинансировании фондом «Династия». © V. A. Ivanov, A. S. Petrovskaya, Yu. E. Skoblo, 2013
+
where Xj — the rate of the creation of atoms in the "j" state; S(Xj) — the sensitivity of the experimental setup; Kjr = Ajf / ^k<j Ajk — the branching coefficient; Ajk — the Einstein coefficient for spontaneous emission; G — the ratio of emitted photons and photons that fall into the entrance slit of the monochromator. In the late afterglow the recombination (2) is the main source of the population of the 3si neon states and the recombination flux into the 3si neon states can be given by the formula:
= <Ne+ [HeNe+]ne,
where agseNe+ — the recombination rate coefficient (2); [HeNe+] and ne — the density of molecular ions HeNe+ and electrons, respectively.
In [4] was established that the 2pi neon atom states are populated by two processes of the dissociative recombination:
aHeNe+
HeNe+ + e —-► Ne(j)* + He; (3)
Ne+
a. 2
Ne+ + e ——► Ne(j)* + He. (4)
Therefore the rate of the population r2Pn of the 2pn states can be expressed as
T2pn = ageNe+ [HeNe+]ne + a^f [Ne+]n
and the ratio of values of the specrtal line intensities which were measured in the experiment can+be given by the ratios of the partial recombination rate coefficients a2pfNe+ /aHseNe+, aNpn+ /a2seNe+ and ion densities [Ne+]/[HeNe+ ]:
NX2Pn K^S(X2pJ fa|eNe+ [Ne+]
NX3s. R'tsS(X3sJ I af;Ne+ + aHeNe+ [HeNe+]1' '
The quasi-stationary approach for the balance equation of ion densities is true under our experimental conditions and therefore the ratio of ion densities is given as [Ne+]/[HeNe+ ] = k5 [Ne]/(aNe2 ne). Taking into accout this ratio equation (5) is presented as the linear dependence of the reciprocal of the electron density
NX2.Pn K^S(X2Pn) (a+B_
N X3s. S (X3s.)
ne
where the coefficients A and B are expressed by the ratios of the recombination rate coefficients ageNe+, a2p2, aHseNe+ and aNe++ :
aHeNe+ aNe+ , rM -,
A = a2p„ fe[Ne]
aHeNe+ ' aHeNe+ aNe+ '
It should be noted that the values of aHeNe+ and a^ were obtained by the same method in [4]. k — the rate constant of the process [5]
HeNe+ + Ne ^ Ne+ + He,
k = (3 ± 1) • 10"11 cm3/s (Tg = 300 K); aNe+
^ a
Ne+
(1.7 ± 0.1) • 10~7 cm3/s is the
rate constant of the dissociative recombination process (4) [6].
In the experiment the relative values of the spectral line intensities of the neon atom and the electron density were measured by the multichannel photon counting method and by the plasma conductivity, respectively. The values of the coefficients A and B were obtained by the ordinary least squares. For the calculation of the coefficients A and B the time dependences of the spectral line intensities of the neon atom (6182, 5852, 6599, 6096, 7245 A; 3s5 ^ 2p9, 2pi ^ 1s2, 2p2 ^ 1s2, 2p4 ^ 1s4, 2p10 ^ 1s4, respectively) were used. It should be noted that the spectral line intensity emitted from the 3s5 into the 2p9 (6182 A) has a much higher value (at time t > 400 ^s) compared with the other spectral lines presented above.
Figure shows the linear dependences of the ratios of the spectral line intensities (emitted in transition 3sj ^ 2pj) on the reciprocal of the electron density. The numerical values of the coefficients A and B are used for the calculation of the partial rate coefficient of
HeNe+ '3s*
The value a
the dissociative recombination a
. , . - . , HeNe+ HeNe+ HeNe+
partial rate coefficients a3s , a3s , a3s
HeNe+ '3s*
was used for the calculation the
into 2s2, 2s3, 2s4 states, respectively.
450 400 350 300
(N
250
rT
200 150 100 50
0
10 15 20 25
1011 cm-3/«
5 10 15 20 25 30 35 1011 cm-3/«
c
300 250 g 200
rT
100 50
0
10
15 101
20 25
cm-3/«
30 35
900
800
700
^ 600 2
5? 500
rT
400
300 200 100
0
10
15 101
20 25
cm-3/n
30 35
The ratio of values of the neon spectral line intensities emitted from radiation trasitions 2pk ^ 1sj and 3si ^ 2pk :
a — 2pi ^ 1s2 and 3s5 ^ 2p9; b — 2p2 ^ 1s2 and 3s5 ^ 2p9; c — 2p4 ^ 1.4 and 3.5 ^ 2p9; d — 2pio ^ 1s4 and 3.S5 ^ 2p9
b
a
5
5
In Table 1. the value of the partial dissociative recombination rate coefficient aHseNe is
presented.
HeNe +
The value of the partial dissociative recombination rate coefficient a3s
Table 1
X2p„ - Ä Transition :2pn —!■ isfc A B, 1011 cm"3 HeNe+ 10-10 cm3/s HeNe+ «3S6 , 10-10 cm3/s
5852 '2pl —>■ 1«2 12.4 ±0.7 12.1 ±0.3 1.90 ±0.09 0.15 ± 0.01
6599 2pn —1«2 15.7 ±0.4 5.2 ± 0.2 2.60 ±0.08 0.166 ± 0.007
6096 ■2Pi —>■ 1«4 37.8 ±0.8 7.3 ±0.3 5.90 ±0.13 0.156 ± 0.005
7245 2pio —1S2 91 ± 2 22.7 ±0.7 16.6 ±0.4 0.182 ± 0.007
The values of partial dissociative rate coefficients which describe the population of the excited neon atom states: 2s2, 2s3, 2s4, were obtained from the ratios of the summary photon values in the late afterglow (500 < t < 8400 ^s).
In the time range (500 < t < 8400 ^s) the temporal dependences of the neon spectral line intensities emitted from the transitions (3sj ^ 2pf ) exhibit a similar behaivior and the source of the population of the 3sj states of the neon atom is the process (3) and then the ratio of the spectral line intensities is given by the formula
NX2Si KgSfrssjag N\ss.
vHeNe+
s (w ) aHeNe+'
where i = 2, 3,4.
The following values were obtained for the ratio of the partial dissociative rate coefficient:
vHeNe+ *3s2
vHeNe+ X3s„.
0.56 ±0.07;
a
HeNe+ ■vHeNe+
0.14 ±0.02;
a
HeNe+ ■3s4
,,HeNe+
0.37 ± 0.04.
As for 4d configuration, it was found that in the afterglow stage 4dn states are populated by the dissociative recombination of the HeNe+ ions with electrons as well:
HeNe+ + e
HeNe+ a4dn
Ne(4dn
He
and the same method was used for obtaining the distribution of recombination fluxes over 4d states of the neon atom.
The distribution of recombination fluxes over 4d states of the neon atom is presented in Table 2.
Table 2
The distribution of recombination fluxes over 4d states of the neon atom
, Â 5343 5341 5764 5820 5330 5913 5748
HeNe+ / HeNe+ «4 d„ /a3sR 0.16 ±0.02 0.40 ± 0.02 0.90 ±0.04 0.68 ±0.02 0.56 ±0.02 0.28 ±0.04 0.72 ± 0.03
Ending of the Table 2
, Â 5906 5656 5902 5116 5918 6182
«4Te+/<Ne+ 0.42 ± 0.02 0.22 ± 0.02 0.39 ±0.02 0.21 ±0.01 0.14 ±0.03 1.00 ±0.03
References
1. Ivanov V. A., Makasyuk I. V. Optimal experiment on studying a non-self-sustained discharge // Rus. Phys. J. 1988. Vol. 31, N 10. P. 43-48.
2. Ivanov V. A., Skoblo Yu. E. Dissociative recombination of heteronuclear molecular ions and electrons in a noble-gas mixture plasma //J. Experimental and Theoretical Physics. 1994. Vol. 79. Iss. 6. P. 921-930.
3. Ivanov V. A., Petrovskaya A. S., Skoblo Yu. E. Population of 2p55s levels of neon in He-Ne plasma: I. The evolution of mechanisms in the discharge and the afterglow // Opt. and Spectroscopy. 2013. Vol. 114, N 4. P. 1-9.
4. Ivanov V. A., Skoblo Yu. E. The dissociative recombination of HeNe+ ions with electrons: The partial rate constants for the formation of atoms in the 2p63p configuration // Rus. J. Phys. Chem. (B). 2012. Vol. 6, N 2. P. 234-238.
5. de Vries G. E, OskamH. G. Recombination and ion-conversion processes in helium-neon mixtures // Phys. Rev. (A). 1970. Vol. 2, N 4. P. 1422-1428.
6. FrommholdL., BiondiM. A., MehrF. J. Electron-temperature dependence of electron-ion recombination in neon // Phys. Rev. 1968. Vol. 165, N 1. P. 44-52.
Статья поступила в редакцию 22 апреля 2013 г.
