Vladimir V Khmelenko

Vladimir V Khmelenko
Texas A&M University | TAMU · Department of Physics and Astronomy

PhD, Doctor of Sciences

About

143
Publications
10,118
Reads
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1,523
Citations
Citations since 2016
35 Research Items
453 Citations
2016201720182019202020212022020406080
2016201720182019202020212022020406080
2016201720182019202020212022020406080
2016201720182019202020212022020406080
Additional affiliations
January 2010 - present
Texas A&M University
January 2007 - present
Rutgers, The State University of New Jersey
January 2006 - present
University of Turku
Education
April 1987 - March 2002
Institute for Energy Problems of Chemical Physics Russian Academy of Sciences
Field of study
  • Chemical Physics
August 1974 - September 1984
Semenov Institute of Chemical Physics
Field of study
  • Chemical Physics
August 1969 - May 1974
Rostov-on Don State University
Field of study
  • Physics

Publications

Publications (143)
Article
Full-text available
Analysis of old and recent experiments on thermoluminescence of cryocrystals and nanoclusters of N2, Ne, Ar, and Kr containing stabilized nitrogen atoms, suggests that the so-called γ-line may correspond to the bound–bound transition 1D–3P of nitrogen anions N− formed in solids by the association of delocalized electrons and metastable nitrogen ato...
Article
We present an experimental study of quantum diffusion of atomic hydrogen in solid H2 films at temperatures below 1K. The atoms are generated via electron impact dissociation by running a continuous rf discharge in helium gas above the H2 film for long (up to 30 days) times. We are able to distinguish between the diffusion of the atoms moving toward...
Article
Full-text available
We report on an electron-spin resonance study of nuclear-polarized phases of hydrogen atoms embedded in solid H2 films at temperatures 0.1–1.5 K and a high magnetic field of 4.6 T. The H atoms in solid H2 were generated by two different dissociation techniques: a cryogenic rf-discharge and bombardment by 5.7 keV electrons via tritium decay. In both...
Article
Determination of the gas temperature in the afterglow plasma jet of pre-cooled helium propagating inside a dense helium vapor at 1.4 K is a difficult task. In this work we analyze the applicability of the emission spectra from oxygen atoms and nitrogen molecules for determination of the local temperature of the gas. Oxygen is always present as a tr...
Preprint
Full-text available
The spectrum of atomic hydrogen has long been viewed as a Rosetta stone that bears the key to decode the writings of quantum mechanics in a vast variety of physical, chemical, and biological systems. Here, we show that, in addition to its role as a basic model of quantum mechanics, the hydrogen atom provides a fundamental building block of quantum...
Article
We report on a direct measurement of the quantum diffusion of H atoms in solid molecular hydrogen films at T=0.7 K. We obtained a rate of pure spatial diffusion of H atoms in the H2 films, Dd=5(2)×10−17 cm2 s−1, which was 2 orders of magnitude faster than that obtained from H atom recombination, the quantity used in all previous work to characteriz...
Article
Full-text available
The spectrum of atomic hydrogen has long been viewed as a Rosetta stone that bears the key to decode the writings of quantum mechanics in a vast variety of physical, chemical, and biological systems. Here, we show that, in addition to its role as a basic model of quantum mechanics, the hydrogen atom provides a fundamental building block of quantum...
Article
We describe the design and construction of an experimental cell for the study of free radicals in macroscopically thick films of solidified molecular and rare gases by 128 GHz Electron Spin Resonance (ESR) at temperatures below 1 K. The ESR resonator has an open Fabry–Pérot design, and its frequency can be tuned in situ by adjusting the spacing bet...
Article
We report on an electron-spin resonance study of nuclear polarization of hydrogen atoms embedded in solid H2 and HD films at temperatures 0.1–1.5 K and in a high magnetic field of 4.6 T. Similar to our previous work [Phys. Rev. Lett. 122, 225301 (2019)], we observed a build-up of the spontaneously (p≃0.35) and highly (p≃0.75) nuclear polarized phas...
Article
Full-text available
Great enhancement of molecular nitrogen luminescence in the afterglow of nitrogen-helium gas mixtures was observed at temperatures ≤ 10 K. The effect is explained by the increased efficiency of the recombination of nitrogen atoms and energy transfer from metastable nitrogen molecules and helium atoms to nitrogen molecules in the cold dense helium v...
Article
Full-text available
Ensembles of nanoclusters created by injection of nitrogen atoms and molecules as well as rare gas (RG) atoms (Ne and Ar) into superfluid ⁴He have been studied via optical and electron spin resonance (ESR) spectroscopies. We studied the dynamics of thermoluminescence spectra emitted during the warming of porous structures formed by nitrogen–neon an...
Article
Full-text available
We report on an experimental observation of two phases of hydrogen atoms in solid H_{2} films at temperatures of 0.1-0.8 K, characterized by a large enhancement of the nuclear spin polarization compared to that given by Boltzmann statistics (p=0.15 at T=0.15 K). The first phase with p=0.35(5) is formed spontaneously during sample storage in a high...
Article
We report on an electron spin resonance study of H and D atoms stabilized in solid mixtures of neon, molecular deuterium, and hydrogen deuteride. We observed that H and D atoms can be stabilized in pure HD and D2 clusters formed in pores of solid Ne as well as in a Ne environment. Raising temperature from 0.1 to 1.3K results in a rapid recombinatio...
Article
Full-text available
We studied the influence of rotation speed of a beaker containing superfluid helium (He II) on the intensity of luminescence of collections of nanoclusters immersed in He II. We observed an increase in the α-group emission of nitrogen atoms ( ² D→ ⁴ S transition) in nanoclusters which correlated with the increasing of rotational speed of the beaker...
Article
Full-text available
We report on an electron spin resonance study of electrons stabilized in solid films of neon–hydrogen mixtures. We found that these films are highly porous and may absorb large amount of liquid helium. We observed that free electrons can be stabilized in two different positions: in a pure neon environment and in \(\hbox {H}_{2}\) clusters formed in...
Article
Full-text available
Our recent experimental work on electron spin waves in atomic hydrogen gas has prompted a revisit of the theory of the identical spin rotation effect (ISRE). A key characteristic determining the properties of the spin waves is the quality factor of ISRE. Unfortunately, calculating this quality factor takes some toil. In this paper we summarize some...
Conference Paper
Full-text available
The helium plasma exhibits a rich network of processes involving energy transfer even at room temperature. Many neutral and ionic states of He atoms and He2 molecules are involved in the energy circulation in helium plasmas at cryogenic temperatures. Nevertheless, optical spectra of excited helium species are almost useless for the temperature dete...
Article
Full-text available
Impurity-helium condensates (IHCs) created by injection of nitrogen atoms and molecules as well as rare gas (RG) atoms (Ne, Ar, and Kr) into superfluid \(^4\)He have been studied via electron spin resonance (ESR) techniques. We investigated the influence of addition of rare gas atoms (Ne, Ar, and Kr) into the condensing \(\hbox {N}_2\)–He gas mixtu...
Article
Full-text available
We present an experimental study of electron spin waves in atomic hydrogen gas compressed to high densities of ~5 × 10¹⁸ cm⁻³ at temperatures ranging from 0.26 to 0.6 K in the strong magnetic field of 4.6 T. Hydrogen gas is in a quantum regime when the thermal de-Broglie wavelength is much larger than the s-wave scattering length. In this regime th...
Preprint
Full-text available
Our recent experimental work on electron spin waves in atomic hydrogen gas has prompted a revisit of the theory of the Identical Spin Rotation Effect (ISRE). A key characteristic determining the properties of the spin waves is the quality factor of ISRE. Unfortunately, calculating this quality factor takes some toil. In this paper we summarize some...
Article
Full-text available
We observed the appearance of a broad feature at 360 nm in spectra obtained during the destruction of ensembles of molecular nitrogen nanoclusters containing stabilized nitrogen, oxygen, hydrogen and deuterium atoms. We attribute this broad feature with a maximum at 360 nm to the N4 polynitrogen molecules which are the product of the neutralization...
Article
Full-text available
We report on an electron spin resonance study of atomic hydrogen stabilized in a solid Ne matrices carried out at a high field of 4.6 T and temperatures below 1 K. The films of Ne, slowly deposited on the substrate at the temperature $\sim$1 K, exhibited a high degree of porosity. We found that H atoms may be trapped in two different substitutional...
Article
Full-text available
We have studied the luminescence of molecular nitrogen nanoclusters containing stabilized nitrogen, oxygen, hydrogen, and deuterium atoms. Optical spectra were observed during the destruction of these ensembles of nanoclusters accompanied by a rapid release of chemical energy stored in the samples. Several interesting features were observed includi...
Article
Full-text available
We report on a study of Dynamic Nuclear Polarization and electron and nuclear spin relaxation of atomic hydrogen and deuterium in solid molecular matrices of H$_{2}$, D$_{2}$, and HD mixtures. The electron and nuclear spin relaxation times ($T_{1e}$ and $T_{1N}$) were measured within the temperature range 0.15-2.5$\,$K in a magnetic field of 4.6 T,...
Article
Full-text available
We studied optical and electron spin resonance spectra during destruction of porous structures formed by nitrogen–rare gas (RG) nanoclusters in bulk superfluid helium containing high concentrations of stabilized nitrogen atoms. Samples were created by injecting products of a radio frequency discharge of nitrogen–rare gas–helium gas mixtures into bu...
Article
Full-text available
In this study argon nanoclusters (800 to∼6500 atoms) formed in supersonic gas jets are compared to the nanoclusters stabilized in superfluid helium. High-energy electron and X-ray diffraction methods are utilized. Both techniques allow investigation of isolated clusters. It is shown that the theoretical prediction of the so-called multiply twinned...
Article
We performed investigations of ensembles of molecular nitrogen nanoclusters, containing stabilized nitrogen atoms, immersed in liquid helium by electron spin resonance and optical spectroscopy. We observed thermoluminescence of nitrogen atoms and molecules via increasing temperature from 1.25 to 4.4 K. Two thermoluminescence maxima were observed, o...
Article
We report on the first ESR study of atomic hydrogen and tritium stabilized in solid T2 and T2:H2 matrices down to 70 mK. The concentrations of T atoms in pure T2 approached 2 × 10(20) cm(-3) (0.60%) and record-high concentrations of H atoms ∼1 × 10(20) cm(-3) (0.33%) were reached in T2:H2 solid mixtures where a fraction of T atoms became converted...
Article
Full-text available
We studied the dynamics of thermoluminescence during destruction of porous structures formed by nanoclusters of nitrogen molecules containing high concentrations of stabilized nitrogen atoms. The porous structures were formed in bulk superfluid helium by injection of the products of discharges in nitrogen–helium gas mixtures through the liquid heli...
Article
We report on a study of the exchange tunneling reaction D + HD → D2 + H in a pure solid HD matrix and in a D2 matrix with a 0.23% HD admixture at temperatures between 130 mK and 1.5 K. We found that the exchange reaction rates, kexHD ∼ 3 × 10(-27) cm(3) s(-1) in the pure HD matrix, and kexD2 = 9(4) × 10(-28) cm(3) s(-1) in the D2 matrix, are nearly...
Article
Full-text available
We report on the measurements of electrons trapped in solid molecular films of H(Formula presented.), HD, and D(Formula presented.). A narrow ESR line associated with the trapped electrons was detected with (Formula presented.), which turned out to be shifted by (Formula presented.)0.3 G from the free electron resonance. Comparison is made with ear...
Article
Full-text available
We report on a study of the exchange tunneling reaction D+HD$\rightarrow$D$_{2}$+H in solid HD at temperatures between 130~mK and 1.5~K by electron spin resonance. The reaction proceeds at almost the same rate ($\sim3\times10^{-27}$cm$^{3}$s$^{-1}$) within this temperature range. This observation differs strongly with the recombination rate of H at...
Article
A low-temperature attachment to a standard ESR spectrometer for the investigation of atoms and radicals trapped in superfluid helium is described. The ESR spectra of nitrogen atoms in He II are obtained for the first time. An analysis of the spectra indicates that under the conditions for accumulation of nitrogen atoms in this work the trapped conc...
Article
Full-text available
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 molecul...
Article
Full-text available
We report on experimental observation of Bose-Einstein condensation (BEC)-like behavior of quantized electron spin waves (magnons) in a dense gas of spin-polarized atomic hydrogen. The magnons are trapped and controlled with inhomogeneous magnetic fields and described by a Schrödinger-like wave equation, in analogy to the BEC experiments with neutr...
Article
We present the first observations of excimer XeO* molecules in molecular nitrogen films surrounding xenon cores of nanoclusters. Multishell nanoclusters form upon the fast cooling of a helium jet containing small admixtures of nitrogen and xenon by cold helium vapor (T = 1.5 K). Such nanoclusters injected into superfluid helium aggregate into porou...
Article
Full-text available
We report on experimental observation of BEC-like behaviour of quantized electron spin waves (magnons) in a dense gas of spin polarized atomic hydrogen. The magnons are trapped and controlled with inhomogeneous magnetic fields, and described by a Schr\"odinger-like wave equation, in analogy to the BEC experiments with neutral atoms. We have observe...
Article
Full-text available
We report on magnetic resonance studies of high-density atomic hydrogen and deuterium in solid hydrogen matrices at temperatures below 1 K. Average concentrations of H atoms ≈3 × 1019 cm−3 are obtained in chemical tunneling reactions of isotope exchange with D atoms. The products of these reactions are closely located pairs of H atoms near D2 molec...
Article
Full-text available
We describe a method for creating a high flux beam of cold atoms and molecules. By using this beam method, spectroscopic studies of the afterglow of oxygen-helium gas mixtures at cryogenic temperatures were performed. The cooling by helium vapor of a helium jet containing trace amounts of oxygen after passing through a radiofrequency discharge zone...
Article
Full-text available
We present the design and performance of an experimental setup for simultaneous electron spin resonance (ESR) and optical studies of nanoclusters with stabilized free radicals at cryogenic temperatures. A gas mixture of impurities and helium after passing through a RF discharge for dissociation of molecules is directed onto the surface of superflui...
Article
Full-text available
We present the design and performance of an experimental cell constructed for matrix isolation studies of H and D atoms in solid H2/D2 films, which are created by molecular beam deposition at temperatures below 1 K. The sample cell allows sensitive weighing of the films by a quartz microbalance (QM) and their studies by magnetic resonance technique...
Article
Full-text available
Impurity-helium condensates created by injection of hydrogen (deuterium) atoms and molecules as well as rare gas (RG) atoms (Ne and Kr) into superfluid 4 He have been studied via electron spin resonance (ESR) techniques. Measurements of the ground-state spectroscopic parameters of hydrogen and deuterium atoms show that the nanoclusters have a shell...
Article
Full-text available
We present investigations of the afterglow of oxygen-helium gas mixtures at cryogenic temperatures. The cooling of a helium jet containing trace amounts of oxygen after passing through a radio frequency discharge zone led to the observation of strong emissions from atomic oxygen. The effect results from the increasing efficiency of energy transfer...
Article
Full-text available
We have studied thermo-stimulated luminenscence and electron emission of nitrogen films and nanoclusters containing free radicals of atomic nitrogen. Thermo-stimulated electron emission from N2 nanoclusters was observed for the first time. Thermo-stimulated luminescence spectra obtained during the destruction of a N2–He sample are similar to those...
Article
Full-text available
Injection of an impurity-helium gas jet passed through a radiofrequency discharge into a volume of superfluid helium leads to the growth of nanoclusters of impurity species which form impurity-helium condensates (IHCs). IHCs are porous materials with very low impurity density (∼1020 cm−3). High average concentrations of stabilized free radicals can...
Article
Full-text available
We present optical spectra of impurity-helium condensates during the process of their formation by injection of gas mixtures N2-Rg-He (Rg=Ne, Kr) into bulk superfluid helium after passing through a RF discharge. Atomic lines of He, Ne, Kr, N, O atoms as well as bands (1+ and 2+ systems of N2) are present in the spectral range 320-1100 nm studied in...
Article
Full-text available
Macroscopic ensembles of weakly interacting argon nanoclusters are studied using x-ray diffraction in low vacuum. As the clusters grow by fusion with increasing temperature, their structure transforms from essentially face-centered cubic (fcc) to hexagonal close packed as the cluster size approaches ∼10^{5} atoms. The transformation involves interm...
Article
Full-text available
Impurity–helium condensates (IHCs) containing nitrogen and krypton atoms immersed in superfluid 4 He have been studied via a CW electron spin resonance (ESR) technique. The IHCs are gel-like aggregates of na-noclusters composed of impurity species. It was found that the addition of krypton atoms to the nitrogen–helium gas mixture used for preparati...