Optical spectroscopy and current detection during warm-up and destruction of impurity–helium condensates
New experimental results on detection of optical spectra and ion currents during destruction of impurity–helium condensates (IHCs) have been obtained. It is shown that emission during IHC sample destruction is accompanied by current pulses, pressure peaks and temperature changes. The molecular ban...
Gespeichert in:
| Datum: | 2015 |
|---|---|
| Hauptverfasser: | , , , , , |
| Format: | Artikel |
| Sprache: | English |
| Veröffentlicht: |
Фізико-технічний інститут низьких температур ім. Б.І. Вєркіна НАН України
2015
|
| Schriftenreihe: | Физика низких температур |
| Schlagworte: | |
| Online Zugang: | http://dspace.nbuv.gov.ua/handle/123456789/127825 |
| Tags: |
Tag hinzufügen
Keine Tags, Fügen Sie den ersten Tag hinzu!
|
| Назва журналу: | Digital Library of Periodicals of National Academy of Sciences of Ukraine |
| Zitieren: | Optical spectroscopy and current detection during warm-up and destruction of impurity–helium condensates / I.N. Krushinskaya, R.E. Boltnev, I.B. Bykhalo, A.A. Pelmenev, V.V. Khmelenko, D.M. Lee // Физика низких температур. — 2015. — Т. 41, № 6. — С. 541-545. — Бібліогр.: 24 назв. — англ. |
Institution
Digital Library of Periodicals of National Academy of Sciences of Ukraine| id |
irk-123456789-127825 |
|---|---|
| record_format |
dspace |
| spelling |
irk-123456789-1278252017-12-29T03:03:17Z Optical spectroscopy and current detection during warm-up and destruction of impurity–helium condensates Krushinskaya, I.N. Boltnev, R.E. Bykhalo, I.B. Pelmenev, A.A. Khmelenko, V.V. Lee, D.M. 10th International Conference on Cryocrystals and Quantum Crystals New experimental results on detection of optical spectra and ion currents during destruction of impurity–helium condensates (IHCs) have been obtained. It is shown that emission during IHC sample destruction is accompanied by current pulses, pressure peaks and temperature changes. The molecular bands of excimer molecules XeO* are assigned to molecules stabilized in films of molecular nitrogen covering the heavier cores of impurity clusters which form impurity–helium condensates. 2015 Article Optical spectroscopy and current detection during warm-up and destruction of impurity–helium condensates / I.N. Krushinskaya, R.E. Boltnev, I.B. Bykhalo, A.A. Pelmenev, V.V. Khmelenko, D.M. Lee // Физика низких температур. — 2015. — Т. 41, № 6. — С. 541-545. — Бібліогр.: 24 назв. — англ. 0132-6414 PACS: 76.30.Rn, 78.60.–b, 61.46.–w http://dspace.nbuv.gov.ua/handle/123456789/127825 en Физика низких температур Фізико-технічний інститут низьких температур ім. Б.І. Вєркіна НАН України |
| institution |
Digital Library of Periodicals of National Academy of Sciences of Ukraine |
| collection |
DSpace DC |
| language |
English |
| topic |
10th International Conference on Cryocrystals and Quantum Crystals 10th International Conference on Cryocrystals and Quantum Crystals |
| spellingShingle |
10th International Conference on Cryocrystals and Quantum Crystals 10th International Conference on Cryocrystals and Quantum Crystals Krushinskaya, I.N. Boltnev, R.E. Bykhalo, I.B. Pelmenev, A.A. Khmelenko, V.V. Lee, D.M. Optical spectroscopy and current detection during warm-up and destruction of impurity–helium condensates Физика низких температур |
| description |
New experimental results on detection of optical spectra and ion currents during destruction of impurity–helium
condensates (IHCs) have been obtained. It is shown that emission during IHC sample destruction is accompanied by
current pulses, pressure peaks and temperature changes. The molecular bands of excimer molecules XeO* are assigned
to molecules stabilized in films of molecular nitrogen covering the heavier cores of impurity clusters which
form impurity–helium condensates. |
| format |
Article |
| author |
Krushinskaya, I.N. Boltnev, R.E. Bykhalo, I.B. Pelmenev, A.A. Khmelenko, V.V. Lee, D.M. |
| author_facet |
Krushinskaya, I.N. Boltnev, R.E. Bykhalo, I.B. Pelmenev, A.A. Khmelenko, V.V. Lee, D.M. |
| author_sort |
Krushinskaya, I.N. |
| title |
Optical spectroscopy and current detection during warm-up and destruction of impurity–helium condensates |
| title_short |
Optical spectroscopy and current detection during warm-up and destruction of impurity–helium condensates |
| title_full |
Optical spectroscopy and current detection during warm-up and destruction of impurity–helium condensates |
| title_fullStr |
Optical spectroscopy and current detection during warm-up and destruction of impurity–helium condensates |
| title_full_unstemmed |
Optical spectroscopy and current detection during warm-up and destruction of impurity–helium condensates |
| title_sort |
optical spectroscopy and current detection during warm-up and destruction of impurity–helium condensates |
| publisher |
Фізико-технічний інститут низьких температур ім. Б.І. Вєркіна НАН України |
| publishDate |
2015 |
| topic_facet |
10th International Conference on Cryocrystals and Quantum Crystals |
| url |
http://dspace.nbuv.gov.ua/handle/123456789/127825 |
| citation_txt |
Optical spectroscopy and current detection during warm-up
and destruction of impurity–helium condensates / I.N. Krushinskaya, R.E. Boltnev, I.B. Bykhalo, A.A. Pelmenev, V.V. Khmelenko, D.M. Lee // Физика низких температур. — 2015. — Т. 41, № 6. — С. 541-545. — Бібліогр.: 24 назв. — англ. |
| series |
Физика низких температур |
| work_keys_str_mv |
AT krushinskayain opticalspectroscopyandcurrentdetectionduringwarmupanddestructionofimpurityheliumcondensates AT boltnevre opticalspectroscopyandcurrentdetectionduringwarmupanddestructionofimpurityheliumcondensates AT bykhaloib opticalspectroscopyandcurrentdetectionduringwarmupanddestructionofimpurityheliumcondensates AT pelmenevaa opticalspectroscopyandcurrentdetectionduringwarmupanddestructionofimpurityheliumcondensates AT khmelenkovv opticalspectroscopyandcurrentdetectionduringwarmupanddestructionofimpurityheliumcondensates AT leedm opticalspectroscopyandcurrentdetectionduringwarmupanddestructionofimpurityheliumcondensates |
| first_indexed |
2025-07-09T07:48:44Z |
| last_indexed |
2025-07-09T07:48:44Z |
| _version_ |
1837154779186331648 |
| fulltext |
© I.N. Krushinskaya, R.E. Boltnev, I.B. Bykhalo, A.A. Pelmenev, V.V. Khmelenko, and D.M. Lee, 2015
Low Temperature Physics/Fizika Nizkikh Temperatur, 2015, v. 41, No. 6, pp. 541–545
Optical spectroscopy and current detection during warm-up
and destruction of impurity–helium condensates
I.N. Krushinskaya
1
, R.E. Boltnev1,2, I.B. Bykhalo
1
, A.A. Pelmenev
1,2
,
V.V. Khmelenko
3
, and D.M. Lee
3
1
Branch of Talroze Institute for Energy Problems of Chemical Physics,
Russian Academy of Sciences, Chernogolovka 142432, Moscow Region, Russia
E-mail: pelmenev@binep.ac.ru
2
Joint Institute for High Temperatures, Russian Academy of Sciences, Moscow 125412, Russia
3
Institute for Quantum Science and Engineering, Department of Physics and Astronomy,
Texas A&M University, College Station, Texas 77843, USA
Received October 30, 2014, published online April 23, 2015
New experimental results on detection of optical spectra and ion currents during destruction of impurity–helium
condensates (IHCs) have been obtained. It is shown that emission during IHC sample destruction is accompanied by
current pulses, pressure peaks and temperature changes. The molecular bands of excimer molecules XeO* are as-
signed to molecules stabilized in films of molecular nitrogen covering the heavier cores of impurity clusters which
form impurity–helium condensates.
PACS: 76.30.Rn Free radicals;
78.60.–b Other luminescence and radiative recombination;
61.46.–w Structure of nanoscale materials.
Keywords: free radicals, optical spectroscopy, condensed helium, nanoclusters.
Introduction
It is well known that deposition of rare gases (RG) passed
through an electrical discharge onto a cold (~ 4 K) surface, or
irradiation of cryofilms by energetic particles (electrons, pro-
tons, or photons with energies of 20 eV–4 MeV) can cause
formation and stabilization of neutral radicals and ions [1–7].
Recent experiments [8] have revealed ion currents ac-
companied by luminescence during destruction of nitrogen–
helium condensates prepared by condensation of nitrogen–
helium gas mixtures (after passing through a radio-frequency
(rf) discharge zone) into bulk superfluid helium (He II). We
present new experimental results on the detection of optical
spectra and ion currents during thermostimulated destruction
of impurity–helium condensates (IHCs) prepared from nitro-
gen–argon–helium and nitrogen–xenon–helium gas mixtures.
Experimental setup
The experimental technique of IHC sample preparation
was first developed in 1974 [9]. A cryogenic portion of the
experimental setup is shown in Fig. 1. It is based on the
injection of a helium gas jet containing impurity particles
(Im = N, N2, H, H2, Ne, Ar, Kr, etc.) into bulk He II. A gas
mixture enters a helium bath region from a quartz capillary
cooled with liquid nitrogen inside an atom source as desig-
nated by position 3 (pos. 3) in Fig. 1(a). The lower portion
of the capillary is surrounded by electrodes (pos. 2 in
Fig. 1(a)) to produce an rf discharge (f = 40–52 MHz, P =
= 40–90 W). The typical conditions during sample pre-
paration were as follows: the impurity admixture,
[Im]/[He] ~ 0.5–1%, the gas jet flux (4.5–6)·10
19
s
–1
, the
superfluid helium temperature 1.5 K, and the duration of the
sample condensation 600–5000 s. Upon fast cooling of the
gas jet, impurity nanoclusters with characteristic size of
5–6 nm form in the gas phase [10,11]. In bulk He II the
nanoclusters aggregate into porous condensates with impuri-
ty particle densities ~ 10
19
–10
20
cm
–3
[10–12].
The oxygen content in the gas mixtures is mainly a re-
sult of contamination of the helium gas. We employ heli-
um gas with an oxygen content of ~10 ppm. A gas jet
(pos. 5 in Fig. 1(a)) consisting of a mixture of helium and
impurity gases was directed onto the surface of superfluid
helium contained in a glass beaker (pos. 6 on Fig. 1(a))
placed below the source at a distance of 20–35 mm. The
mailto:pelmenev@binep.ac.ru
I.N. Krushinskaya, R.E. Boltnev, I.B. Bykhalo, A.A. Pelmenev, V.V. Khmelenko, and D.M. Lee
542 Low Temperature Physics/Fizika Nizkikh Temperatur, 2015, v. 41, No. 6
steady state level of He II in the beaker (with the inner
diameter of 40 mm) was maintained by a fountain pump
situated in the main liquid helium bath in the glass dewar.
Calibrated Lake Shore thermometers were used for the
temperature measurements. The pressure of the helium
vapor in the dewar was measured with a RoseMount gauge
S3051TA2 calibrated to work within the range 0–10 kPa.
One setup modification has been done to extend the ac-
cessible spectral range to the UV range. The sample emis-
sion was directly collected by an optical fiber (pos. 4 in
Fig. 1(a)) fixed above an IHC sample in the beaker,
Fig. 1(b). The emission passed through fibers (inside and
outside of the cryostat) and a vacuum feed-through to the
AvaSpec-ULS2048XL-USB2 spectrometer. The spectrome-
ter, the vacuum feed-through, and the fibers all together
were calibrated for absolute intensity measurements by a
light source AvaLight-DH-BAL-CAL. The spectrometer
allowed us to detect luminescence within the spectral range
from 200 to 1100 nm with resolution ~2.5 nm.
The ion currents accompanying the destruction of impu-
rity–helium samples were collected by an electrode (a stain-
less steel disc, pos. 7 in Fig. 1(a)) connected directly to a
picoammeter (Keithley 6485).
Experimental results and discussion
Firstly, we compare warm-ups of two samples prepared
from a [N2]/[Ar]/[He] = 1/10/1000 gas mixture (Fig. 2).
The first sample has been condensed without action of an
rf discharge, while the second one has been prepared from
a gas mixture passed through the rf discharge zone. The
sample destruction process was started after the onset of
evaporation of liquid helium from the beaker. When there
was no liquid helium in the bottom part of the dewar, the
presence of liquid helium in the beaker could be monitored
by the relation between the temperature measured in the
beaker and the pressure detected in the helium dewar (the
saturated helium vapor pressure). A characteristic feature
of the IHC destruction process is a pressure peak corre-
sponding to sublimation of helium atoms bound to the im-
purity nanocluster surfaces. These features can be seen for
both samples in Fig. 2 (at t = 370 and 280 s, correspond-
ingly), while the luminescence due to excited atomic and
molecular species can be observed only from the IHCs
prepared with an rf discharge. The luminescence intensity
corresponds to the integrated (in the range from 220 to
1080 nm) luminescence intensity.
The spectra of luminescence detected during the de-
struction of the second sample at times 1 and 2 (the points
marked at Fig. 2(b)) are shown in Fig. 3. There are some
differences in the spectra. The -group (corresponding to
the
1
S–
1
D transition of O atoms) and the Vegard–Kaplan
Fig. 1. (a) Scheme of the cryogenic part of the experimental
setup: atom source (1), electrodes for an rf discharge (2), liquid
nitrogen (3), optical fiber (4), gas jet (5), beaker for sample
condensation (6), ion collector (7), thermometer (8), fountain
pump in the main helium bath (9), nitrogen dewar (10), helium
dewar (11); (b) Photo of the end of the atom source with beaker
showing the position of the fiber collecting emission from IHC
sample. Red laser beam illuminates the anode, showing the
region of sample destruction.
Fig. 2. (Color online) The temporal dependences of the tempera-
ture, pressure, current, and integrated luminescence intensity
(brown, green, blue, and magenta lines, respectively) during de-
struction of sample prepared from a gas mixture [N2]/[Ar]/[He] =
= 1/10/1000: (a) the mixture condensed without action of the rf
discharge; (b) the mixture passed through an rf discharge zone.
Optical spectroscopy and current detection during warm-up and destruction of impurity–helium condensates
Low Temperature Physics/Fizika Nizkikh Temperatur, 2015, v. 41, No. 6 543
(VK) bands of N2 dominate in the earlier spectrum, while
the more intense -group, and the -system bands of NO
molecules, together with the -group of atomic nitrogen
(corresponding to the transition
2
P–
2
D), dominate in the
second spectrum detected during the final, brightest, flash.
The relatively weak -group of atomic nitrogen, corre-
sponding to the forbidden transition
2
D–
4
S, was present in
both spectra. The dominance of emission due to species
containing oxygen can be explained by a multishell struc-
ture of impurity clusters [13–16]: heavier particles (in this
case O atoms) are involved in the reactions and the lumi-
nescence at the final stage of sample destruction when im-
purity clusters melt and fuse together.
The temporal dependences of the temperature, pressure,
current, and integrated luminescence intensity during de-
struction of the sample prepared from a gas mixtures
[N2]/[Xe]/[He] = 1/1/400 are shown in Fig. 4(a). In this case
the sample destruction process was started in He II as the
liquid helium level decreased in the beaker. The orange ver-
tical line marks the moment when liquid helium is gone
from the beaker with the sample (He II had been pumped
away from the main helium bath of the cryostat earlier). As
one can see from Figs. 2 and 4(a), the destruction of impuri-
ty–helium condensates occurs through successive explosions
of the “hottest” sample fragments, accompanied by peaks of
temperature and pressure. After evaporation of LHe from
the beaker, the sample temperature is kept stable due to
evaporation of “weakly bound helium” — i.e., liquid helium
contained in the sample pores [17]. At this stage, the sample
annealing is accompanied by shrinking of the sample due to
capillary forces. IHC samples shrink up to 10-fold [17],
much more than highly porous aerogels (with a porosity of
95–99.5 %) [18,19], and become much denser (the impurity
particle density increases up to ~10
21
cm
–3
[20]). When the
Fig. 3. (Color online) Luminescence spectra detected at the mo-
ments 1 and 2 (shown in Fig. 2(b)) during destruction of the sam-
ple prepared from a gas mixture [N2]/[Ar]/[He] = 1/10/1000
passed through an rf discharge area.
Fig. 4. (Color online) (a) The temporal dependences of the temperature (1), pressure (2), current (3), and integrated luminescence inten-
sity (4) (brown, green, blue, and magenta line, respectively) during destruction of sample prepared from a gas mixture [N2]/[Xe]/[He] =
= 1/1/400 passed through an rf discharge zone. The orange vertical line shows the time when liquid helium had completely evaporated
from the beaker. (b) Photo of the third flash (at t = 323 s).
I.N. Krushinskaya, R.E. Boltnev, I.B. Bykhalo, A.A. Pelmenev, V.V. Khmelenko, and D.M. Lee
544 Low Temperature Physics/Fizika Nizkikh Temperatur, 2015, v. 41, No. 6
sample become “dry” (no liquid helium in the pores re-
mains), the beaker containing the sample starts to warm up
because of heat transfer from the atom source. The warm-up
causes sublimation of “strongly bound helium” — helium
adsorbed on the impurity nanocluster surface [17,20] and
coalescence of the nanoclusters into microcrystals [10,21].
The sublimation of helium shells, which had prevented re-
combination of radicals trapped on the impurity nanoclusters
also initiates chemical reactions, and the formation of exci-
ted species responsible for optical emission during the sam-
ple destruction. The sublimation of helium atoms from the
impurity nanocluster surface is revealed by the pressure
peak, with a subsequent decrease of the pressure to zero
(Figs. 2 and 4(a)).
A photo of the explosion (which corresponds to the flash
#3, at t = 323 s) of the nitrogen–xenon–helium sample is
shown in Fig. 4(b). As one can see the whole volume of the
beaker is filled with glowing dust particles. The spectrum of
this flash is shown in Fig. 5 (red line) together with the lu-
minescence spectrum during destruction of the sample pre-
pared from the gas mixture [Xe]/[N2]/[He] = 1/10/2000
(blue line, the emission for wavelengths shorter than 310 nm
is cut off due to the glass of the dewars). The intense
Vegard–Kaplan bands, -, -, and -groups were observed
along with the “green bands” and a band at 595 nm, corre-
sponding, possibly, to the cascade transitions of the XeO*
molecule, XeO*(2
1
–1
1
) and Xe
+
O
–
(3
1
+
–2
1
) [22]. The
band at 595 nm has never been observed from XeO* in the
gas phase, nor have the transitions from XeO(2
1
) in a xen-
on matrix [22,23]. We can see that the decrease of the xenon
content in the condensed gas mixture is accompanied by a
gain of the XeO* molecule emission because single Xe and
O atoms reside over a larger volume (nitrogen matrix) with
increase of nitrogen content. Therefore, for the first time the
XeO* spectra have been observed from molecules captured
in N2 films surrounding the xenon cores of impurity
nanoclusters.
The current pulses with amplitudes ~ 1 nA of positive
and negative polarities were detected during destruction of
the IHC samples under study. We suggest that electrons
were carriers of negative charge, while the origin of posi-
tive carriers is still unclear. The ions can be formed (due to
Penning ionization processes) and trapped into impurity
nanoclusters growing in a gas jet [24]. Another possibility
for ion formation is irradiation of impurity nanoclusters
stabilized in bulk He II by VUV emission from the dis-
charge area.
Conclusions
The destruction of impurity–helium condensates con-
taining stabilized radicals is accompanied with pressure
and luminescence peaks, and current pulses (~ nA).
The final pressure peak during sample destruction cor-
responds to sublimation of helium shells bound to the im-
purity nanocluster surface. The sublimation of helium
shells which had prevented recombination of radicals
trapped on the impurity nanoclusters initiates chemical
reactions and the formation of excited species responsible
for optical emission during the sample destruction.
The spectra observed during destruction of impurity–
helium condensates containing stabilized radicals reveal
that all of the emitting particles are localized within solid
matrices. The spectral changes observed during the de-
structions of IHC samples confirm the multishell structure
Рис. 5. (Color online) Luminescence spectra detected during destruction of samples prepared from gas mixtures [Xe]/[N2]/[He] =
= 1/1/400 (red line) and [Xe]/[N2]/[He] = 1/10/2000 (blue line).
Optical spectroscopy and current detection during warm-up and destruction of impurity–helium condensates
Low Temperature Physics/Fizika Nizkikh Temperatur, 2015, v. 41, No. 6 545
of impurity nanoclusters which form IHCs. The cluster
growth occurs in the cold helium jet [11] when the heavier
impurity particles form a cluster core which is later cov-
ered with lighter impurity particles.
The spectra of XeO* molecules captured in N2 films
have been observed for the first time.
Acknowledgments
This study was supported by the Program “Matter at
High Energy Densities” of the Presidium of the Russian
Academy of Sciences and by NSF grant No. DMR
1209255.
1. Formation and Trapping of Free Radicals, A.M. Bass and
H.P. Broida (eds.), Academic Press (1960).
2. W.V. Bouldin and W. Gordy, Phys. Rev. 135, A 806 (1964).
3. V.E. Bondybey, M. Rasanen, and A. Lammers, Annu. Rep.
Prog. Chem., Sect. C 95, 331 (1999).
4. L. Andrews, Ann. Rev. Phys. Chem. 30, 79 (1979).
5. L.B. Knight, Acc. Chem. Res. 19, 313 (1986).
6. M.E. Jacox and W.E. Thompson, Research on Chemical
Intermediates 12, 33 (1989).
7. A.N. Ogurtsov, E.V. Savchenko, M. Kirm, B. Steeg, and
G. Zimmerer, J. Electron Spectrosc. Relat. Phenom. 101,
479 (1999).
8. R.E. Boltnev, I.B. Bykhalo, I.N. Krushinskaya, A.A. Pelmenev,
V.V. Khmelenko, D.M. Lee, I.V. Khyzhniy, S.A. Uyutnov,
E.V. Savchenko, A.N. Ponomaryov, G.B. Gumenchuk, and
V.E. Bondybey, Fiz. Nizk. Temp. 39, 580 (2013) [Low Temp.
Phys. 39, 451 (2013)].
9. E.B. Gordon, L.P. Mezhov-Deglin, and O.F. Pugachev,
JETP Lett. 19, 103 (1974).
10. V. Kiryukhin, B. Keimer, R.E. Boltnev, V.V. Khmelenko,
and E.B. Gordon, Phys. Rev. Lett. 79, 1774 (1997).
11. V. Kiryukhin, E.P. Bernard, V.V. Khmelenko, R.E. Boltnev,
N.V. Krainyukova, and D.M. Lee, Phys. Rev. Lett. 98,
195506 (2007).
12. S.I. Kiselev, V.V. Khmelenko, D.M. Lee, V. Kiryukhin, R.E.
Boltnev, E.B. Gordon, and B. Keimer, Phys. Rev. B 65,
024517 (2001).
13. O.G. Danylchenko, Yu.S. Doronin, S.I. Kovalenko, and
V.N. Samovarov, JETP Lett. 84, 324 (2006).
14. T. Laarmann, H. Wabnitz, K. von Haeften, and T. Möller,
J. Chem. Phys. 128, 014502 (2008).
15. R.E. Boltnev, V.V. Khmelenko, and D.M. Lee, Fiz. Nizk.
Temp. 36, 484 (2010) [Low Temp. Phys. 36, 382 (2010)].
16. V.V. Khmelenko, A.A. Pelmenev, I.N. Krushinskaya, I.B.
Bykhalo, R.E. Boltnev, and D.M. Lee, J. Low Temp. Phys.
171, 302 (2013).
17. R.E. Boltnev, E.B. Gordon, I.N. Krushinskaya, M.V.
Martynenko, A.A. Pelmenev, E.A. Popov, V.V. Khmelenko,
and A.F. Shestakov, Fiz. Nizk. Temp. 23, 753 (1997) [Low
Temp. Phys. 23, 567 (1997)].
18. T. Herman, J. Day, and J. Beamish, Phys. Rev B 73, 094127
(2006).
19. H. Kato, W. Miyashita, R. Nomura, and Y. Okuda, J. Low
Temp. Phys. 148, 621 (2007).
20. E.P. Bernard, R.E. Boltnev, V.V. Khmelenko, V. Kiryukhin,
S.I. Kiselev, and D.M. Lee, J. Low Temp. Phys. 134, 169
(2004).
21. N.V. Krainyukova, R.E. Boltnev, E.P. Bernard, V.V.
Khmelenko, D.M. Lee, and V. Kiryukhin, Phys. Rev. Lett.
109, 245505 (2012).
22. A.G. Belov and E.M. Yurtaeva, Fiz. Nizk. Temp. 27, 1268
(2001) [Low Temp. Phys. 27, 938 (2001)].
23. W.G. Lawrence and V.A. Apkarian, J. Chem. Phys. 97, 2229
(1992).
24. A.A. Pelmenev, I.N. Krushinskaya, I.B. Bykhalo, and R.E.
Boltnev, On Charged Impurity Structures in Liquid Helium,
to be published.
|