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May 2010

Volume 36, Issue 5, pp. 363-473


PREFACE

Low Temp. Phys. 36, 363 (2010); http://dx.doi.org/10.1063/1.3432240 (2 pages)

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01.30.-y Physics literature and publications

Low-temperature radial thermal expansion of single-walled carbon nanotube bundles saturated with nitrogen

A. V. Dolbin, V. B. Esel’son, V. G. Gavrilko, V. G. Manzhelii, S. N. Popov, N. A. Vinnikov, and B. Sundqvist

Low Temp. Phys. 36, 365 (2010); http://dx.doi.org/10.1063/1.3432241 (5 pages) | Cited 2 times

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The effect of N2 impurity on the radial thermal expansion coefficient αr of single-walled carbon nanotube bundles has been investigated in the temperature interval 2.2–43 K by the dilatometric method. Saturation of nanotube bundles with N2 sharply increased the positive values of αr in the entire experimental temperature range and resulted in a very high, wide maximum in the thermal expansion coefficient αr(T) at T ∼ 28 K. Low-temperature impurity desorption from N2-saturated powder consisting of bundles of single-walled carbon nanotubes with open and closed ends has been investigated.
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65.40.De Thermal expansion; thermomechanical effects
68.43.Nr Desorption kinetics
61.72.S- Impurities in crystals

Novel mechanism of the negative thermal expansion of doped fullerite C60

M. A. Strzhemechny and I. V. Legchenkova

Low Temp. Phys. 36, 370 (2010); http://dx.doi.org/10.1063/1.3432243 (3 pages)

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A model of an atomic impurity in an octahedral void of fullerite C60 is suggested. The problem is solved in the spherical oscillator approximation, which is appropriate for the larger rare gas atoms. It is shown that such impurities can contribute to the negative thermal expansion at low temperatures and produce a Schottky-like maximum at higher temperatures.
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65.40.De Thermal expansion; thermomechanical effects
61.72.U- Doping and impurity implantation
61.72.Qq Microscopic defects (voids, inclusions, etc.)

Raman spectroscopy of DNA-wrapped single-walled carbon nanotube films at 295 and 5 K

V. A. Karachevtsev and A. Yu. Glamazda

Low Temp. Phys. 36, 373 (2010); http://dx.doi.org/10.1063/1.3432244 (9 pages)

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Resonance Raman spectra of DNA-wrapped single-walled carbon nanotubes films were studied at 5 and 295 K in the range of radial-breathing (175–320 cm−1) and tangential (1520–1625 cm−1) modes. The spectra were compared with those of nanotubes in bundles. At 5 K in the spectrum of film an upshift of bands with respect to their spectrum at high temperature and the intensity redistribution among bands of two samples were observed. The magnitude of this upshift depends on the nanotube type. The influence of a temperature decrease, the environment, and the electron-phonon coupling on the Raman spectrum of nanotubes are discussed.
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78.30.-j Infrared and Raman spectra
61.48.De Structure of carbon nanotubes, boron nanotubes, and other related systems
63.20.kd Phonon-electron interactions

Stabilization of H and D atoms in krypton–helium nanocondensates

R. E. Boltnev, V. V. Khmelenko, and D. M. Lee

Low Temp. Phys. 36, 382 (2010); http://dx.doi.org/10.1063/1.3432245 (10 pages)

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Impurity–helium condensates formed by krypton nanoclusters containing atoms and molecules of hydrogen isotopes have been studied via an electron spin resonance (ESR) technique. Analysis of the ESR spectra has shown that most of the H and D atoms reside on the surfaces of Kr nanoclusters. Very large average concentrations have been obtained for H atoms (1.2⋅10⋅19 cm−3) and D atoms (3.3⋅19 cm−3) in these experiments. Line narrowing has been observed for the highest concentration of D atoms stabilized in the Kr–He sample. Exchange tunneling reactions have been studied in Kr–He sample containing H and D atoms.
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61.72.U- Doping and impurity implantation

Infrared studies of ortho-para conversion at Cl-atom and H-atom impurity centers in cryogenic solid hydrogen

P. L. Raston, S. C. Kettwich, and D. T. Anderson

Low Temp. Phys. 36, 392 (2010); http://dx.doi.org/10.1063/1.3432246 (8 pages)

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We report infrared spectroscopic studies of H2 ortho-para (o/p) conversion in solid hydrogen doped with Cl-atoms at 2 K while the Cl+H2 (v = 1)→HCl+H infrared-induced chemical reaction is occurring. The Cl-atom doped hydrogen crystals are synthesized using 355 nm in situ photodissociation of Cl2 precursor molecules. For hydrogen solids with high ortho-H2 fractional concentrations (Xo = 0.55), the o/p conversion kinetics is dominated by Cl-atom catalyzed conversion with a catalyzed conversion rate constant Kcc = 1.16(11) min−1 and the process is rate-limited by ortho-H2 quantum diffusion. For hydrogen crystals with low ortho-H2 concentrations (Xo = 0.03), single-exponential decay of the ortho-H2 concentration with time is observed which is attributed to H-atom catalyzed o/p conversion by the H-atoms produced during the infrared-induced Cl+H2 reaction. The measured H-atom catalyzed o/p conversion kinetics indicates the H-atoms are mobile under these conditions in agreement with previous ESR measurements.
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67.80.fh Atomic hydrogen and isotopes
07.20.Mc Cryogenics; refrigerators, low-temperature detectors, and other low-temperature equipment
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
82.20.Xr Quantum effects in rate constants (tunneling, resonances, etc.)
82.30.Nr Association, addition, insertion, cluster formation
78.30.Hv Other nonmetallic inorganics
71.55.Ht Other nonmetals
66.30.J- Diffusion of impurities

Local formation of HArF in solid argon: Low-temperature limit and thermal activation

H. Lignell, L. Khriachtchev, A. Lignell, and M. Räsänen

Low Temp. Phys. 36, 400 (2010); http://dx.doi.org/10.1063/1.3432248 (7 pages) | Cited 3 times

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The H+Ar+F reaction leading to HArF formation in an argon matrix is studied at temperatures down to 8 K. The effects of the precursor concentration, deuteration, IR light, and deposition temperature as well as thermal activation of this reaction are studied. It is found that HArF molecules are formed slowly but efficiently at 8 K in a photolyzed HF/Ar matrix, supporting the previously reported results. The formation rate of HArF (and DArF) exhibits a low-temperature limit and enhances at elevated temperatures with activation energy of about 40 meV. All the data show that HArF is formed as a result of a local reaction of hydrogen atoms with the parent Ar–F centers and the tunneling mechanism is very probable here. The locality of the precursor photolysis required for this tunneling reaction is consistent with the partial HArF formation observed during photolysis of HF in an argon matrix. The decay mechanism of (ArHAr)+ cations is also studied. The present results confirm the previous conclusions that the decay of the cations is not essential to HArF formation.
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82.50.Bc Processes caused by infrared radiation
78.30.Hv Other nonmetallic inorganics

Formation of (Xe2H)* centers in solid Xe via recombination: nonstationary luminescence and internal electron emission

E. V. Savchenko, I. V. Khyzhniy, S. A. Uyutnov, G. B. Gumenchuk, A. N. Ponomaryov, M. K. Beyer, and V. E. Bondybey

Low Temp. Phys. 36, 407 (2010); http://dx.doi.org/10.1063/1.3432249 (4 pages)

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The formation of excimers (Xe2H)* in solid Xe doped with molecular hydrogen under irradiation by an electron beam is studied using the original two-stage technique of nonstationary (NS) cathodoluminescence (CL) in combination with current activation spectroscopy—thermally stimulated exoelectron emission (TSEE). Charged species are generated using a high-density electron beam. The species produced are probed with a low-density beam with sample gradually heated. The near-UV emission of the (Xe2H)* is used to monitor the neutralization process. It is found that the temperature behavior of the NS CL band of (Xe2H)* clearly correlates with the yield of TSEE measured after identical pre-irradiation of the sample. The fingerprints of the thermally stimulated detrapping of electrons—«internal electron emission»—-in the spectrum of NS CL point to the essential role of the neutralization reaction in the stability of protons solvated by rare-gas atoms.
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79.75.+g Exoelectron emission
78.60.Hk Cathodoluminescence, ionoluminescence

Ion–molecule reactions of CoAr6+ with nitrogen oxides N2O, NO, and NO2: measuring absolute pressure by shock-freezing of the collision complex

C. van der Linde, R. F. Höckendorf, O. P. Balaj, and M. K. Beyer

Low Temp. Phys. 36, 411 (2010); http://dx.doi.org/10.1063/1.3432259 (6 pages) | Cited 2 times

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A new method to determine the absolute pressure in an ultra-high vacuum apparatus is tested using ion molecule reactions with CoAr6+. In a collision with a neutral reactant the complex between Co+ and the collision partner is stabilized by evaporation of argon atoms. If CoAr6+ reacts at the collision rate, the absolute pressure can be determined by comparing the experimental collision rate with the collision rate calculated from average dipole orientation theory. The experimental results with N2O, NO and NO2 do indeed show that the collision complex is frozen out. Comparing the rates of primary, secondary and tertiary reaction products suggests that not all collisions of CoAr6+ are reactive.
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82.30.Fi Ion-molecule, ion-ion, and charge-transfer reactions
47.80.Fg Pressure and temperature measurements

Crystal field splitting on D↔S transitions of atomic manganese isolated in solid krypton

O. Byrne, M. A. Collier, M. C. Ryan, and J. G. McCaffrey

Low Temp. Phys. 36, 417 (2010); http://dx.doi.org/10.1063/1.3432260 (7 pages)

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Narrow excitation features present on the [Ar]3d64s1a6D(J = 9/2−1/2)←[Ar]3d54s2a6S1/2 transitions of manganese atoms isolated in solid Kr are analyzed within the framework of weak crystal field splitting. Use of the Wp optical lineshape function allowed identification of multiple zero-phonon lines for individual spin-orbit J states of the a a6D←a6S transition recorded with laser-induced excitation spectroscopy. Excellent agreement exists between the predicted crystal field splitting patterns for the J levels of the a6D state isolated in the «red» tetravacancy site of solid Kr. The tetrahedral crystal field of the «red» trapping site splits J>3/2 levels of the a6DJ and a4D7/2 states by approximately 30 cm−1. This report represents the first definitive evidence of crystal field splitting, induced by the weak van der Waals interactions between a neutral metal atom and the rare gas atoms surrounding it in a well-defined solid-state site.
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71.70.Ch Crystal and ligand fields
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect
61.72.jd Vacancies

Lattice phonons of solid phases (α,β,δ,ε) of carbon monoxide by optical studies

A. Serdyukov, M. Vetter, A. Brodyanski, and H. J. Jodl

Low Temp. Phys. 36, 424 (2010); http://dx.doi.org/10.1063/1.3432267 (15 pages)

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The phase diagram of solid carbon monoxide was investigated in the pressure range 0–10 GPa and temperature range 30–300 K by infrared and Raman spectroscopy. The tentative phase diagram known from the literature was expanded and specified in detail. The δ-phase region is divided into two subphases—δrot and δloc—similar to solid nitrogen. The pressure-temperature behavior of the elementary and combined excitations was also followed up. The vibron overtone region was carefully investigated by FTIR spectroscopy as a function of temperature at different pressures; the fundamental region was investigated by Raman spectroscopy. The features of the IR-active phonon sideband to the vibron overtone were investigated in detail in the entire pressure-temperature region. The lattice-phonon spectra were studied by Raman spectroscopy as a function of pressure (at lowest temperature) and by IR spectroscopy as a function of temperature at saturated vapor pressure.
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63.20.K- Phonon interactions
78.30.Hv Other nonmetallic inorganics
81.30.Dz Phase diagrams of other materials
62.50.-p High-pressure effects in solids and liquids

Study of cluster formation in low-temperature systems. Spectral manifestation of resonance dipole–dipole interactions between nondipole polyatomic molecules

A. N. Cherevatova, V. N. Bocharov, T. D. Kolomiitsova, D. N. Shchepkin, and K. G. Tokhadze

Low Temp. Phys. 36, 439 (2010); http://dx.doi.org/10.1063/1.3432261 (9 pages)

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Resonance dipole-dipole interactions are shown to strongly manifest themselves in fundamental and overtone band shapes of low-temperature systems consisting of polar and nonpolar molecules as well with a relatively large first derivatives (P′>0.3 D) of the dipole moment. A rough model on the basis of the interaction between two non-degenerate, doubly degenerate, and triply degenerate oscillators was developed to study pairs of interacting molecules and clusters in low-temperature condensed systems. The concentration dependences of second- and third-order spectral band moments made it possible to estimate the number of molecules in clusters.
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36.40.-c Atomic and molecular clusters
33.15.Kr Electric and magnetic moments (and derivatives), polarizability, and magnetic susceptibility

Single-molecule probing of incommensurate biphenyl

M. Pärs, V. Palm, and J. Kikas

Low Temp. Phys. 36, 448 (2010); http://dx.doi.org/10.1063/1.3432262 (3 pages)

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Our data on the distribution of purely electronic linewidths of single molecules of terrylene in incommensurate biphenyl crystals are compared with the data obtained by other groups for different low-temperature organic solid hosts and with results of numerical simulations. The first two moments of the distributions measured within a narrow temperature interval have been used to calculate a single dimensionless parameter characterizing each of the respective hosts—the variation coefficient. It appears that different amorphous hosts have similar values of this coefficient, but the value obtained for the incommensurate crystal of biphenyl is significantly different. One can conclude that the remarkable single-molecule line broadening in biphenyl at 1.8 K cannot be solely explained by the interaction with two-level systems, which is considered to cause the broadening in amorphous hosts.
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33.70.Jg Line and band widths, shapes, and shifts

Unveiled optical properties of tetrapyrollic pigments in cryogenic environments

C. Crépin, N. Shafizadeh, W. Chin, J.-P. Galaup, J. G. McCaffrey, and S. M. Arabei

Low Temp. Phys. 36, 451 (2010); http://dx.doi.org/10.1063/1.3432263 (7 pages) | Cited 1 time

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An unexpected phenomenon was revealed in the laser induced fluorescence spectra of free-base (H2Pc) and zinc (ZnPc) phthalocyanines trapped in rare gas and nitrogen matrices under a moderate increase in the laser intensity. In all matrices the intensity of an emission band near 755 nm increased drastically when pumping the S1←S0 transition. This observation was assigned to stimulated emission in a four-level scheme involving a vibronic transition from the lowest electronic state to a vibrational level of the ground state. In the present work, we expose new similar results obtained with porphyrin molecules, i.e. tetra-benzoporphin (TBP). With free-base H2TBP, stimulated emission was observed in Ar or N2 matrices, but not in Xe matrices. A possible reason could be a fast inter-system crossing rate due to the heavy atom effect induced by Xe. We also report the observation of persistent burnt spectral holes, although the low efficiency of this process is not competitive with stimulated emission and no decrease of the stimulated emission with time was observed. With ZnTBP no stimulated emission could be recorded but the appearance of rather strong phosphorescence was noticed. Similar studies focusing on the stimulated emission phenomenon is that they should allow new insights into site effects and site selectivity.
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78.45.+h Stimulated emission
78.60.-b Other luminescence and radiative recombination
78.55.-m Photoluminescence, properties and materials

Conformations of ribonucleoside uridine in the low temperature Ar matrices

A. Yu. Ivanov

Low Temp. Phys. 36, 458 (2010); http://dx.doi.org/10.1063/1.3432264 (7 pages)

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The conformational equilibrium of the ribonucleoside uridine molecules in low-temperature Ar matrices was investigated by the FTIR matrix isolation spectroscopy and quantum-chemical calculations at the DFT and MP2 levels of theory. It was established that conformers with a carbonyl group C2O, which takes part in the intramolecular hydrogen bonds, dominate in the low temperature matrices. Populations of syn- and anti- conformers with intramolecular hydrogen bonds O5′H–O2 and O2′–O2, respectively, are equal practically. Unlike 2′-deoxyuridine, the syn- conformers of Ur with C3′-endo structure of the ribose ring (South) have been found in Ar matrices. At the same time the conformations of C2′-endo (North) ribose ring prevail both in anti- and syn- conformers.
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61.50.Lt Crystal binding; cohesive energy

Spectroscopy and micro-luminescence mapping of Xe-implanted defects in diamond

Y. Deshko and A. A. Gorokhovsky

Low Temp. Phys. 36, 465 (2010); http://dx.doi.org/10.1063/1.3432265 (7 pages)

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Ion implantation in diamond creates optically active defects which have emission lines in broad spectral regions and may be used in advanced photonics and optical communication applications. A brief review of the photoluminescence properties of Xe+ ion implanted diamond is presented. The Xe-related center is of particular interest as this center is one of a few centers (Ni, Si, Cr) in diamond having sharp emission lines in the infrared spectral region, specifically at 813 and 794 nm. The paper discusses an approach to determine the important and difficult to measure conversion efficiency of implanted ions into emitting optical centers. The method uses micro-luminescence confocal mapping and statistical analysis based on a compound Poisson distribution, accounting for both the implanted centers and the optically excited centers statistics. Results of numerical simulations and experimental measurements are presented.
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81.05.ug Diamond
78.55.Hx Other solid inorganic materials
78.30.Na Fullerenes and related materials
61.72.up Other materials
61.72.jn Color centers
02.70.Rr General statistical methods
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Anniversary of the B. Verkin Institute for Low Temperature Physics and Engineering of the National Academy of Sciences of Ukraine

Low Temp. Phys. 36, 472 (2010); http://dx.doi.org/10.1063/1.3432266 (2 pages)

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Abstract Unavailable
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07.20.Mc Cryogenics; refrigerators, low-temperature detectors, and other low-temperature equipment
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