D. Yu. Dubov

Laboratory and in situ evidence for the presence of ice particles in a PMSE region

An interpretation is made of rocket data obtained from an electric field mill (EFM) sensor during the international rocket-radar campaign NLC-91. The interpretation is based on a laboratory study of the interaction of a water particle beam with the EFM recovered after the rocket flight. Both rocket and laboratory data show that the field mill is sensitive to ice microparticle impacts and that perturbations in the EFM signal observed in the vicinity of noctilucent clouds and an enhanced radar echo (PMSE) layer are caused not only by atmospheric electric fields but also by the impact of solid particles. The altitude range of the impact signatures suggests the presence of ice particles in the PMSE region above the height of the optically detected noctilucent clouds. The analysis of the rocket data on the basis of the laboratory results allows us to estimate sizes of these PMSE particles to be 13–40 nm.

Clustering in molecular gases freely expanding into vacuum

The actual enthalpies and entropies of clustering and the properties of clusters characterizing their catalytic effect on the rate of relaxation of vibrational degrees of freedom are used to compute (N2O)N and (CO2)N cluster formation and growth in gases expanding into a vacuum through a sonic nozzle. Relations are found between characteristics of gaseous N2O and CO2 in the nozzle source and in the jet flow containing clusters and those of the molecular cluster beam formed from the axial region of the jet. Calculated and measured values of the following cluster-beam characteristics are compared: intensity, flux density for molecules in the beam, scaling parameters for transition to well-developed condensation in the jet, cluster size distribution function, mean cluster size, and internal cluster temperature. Realistic characterization of cluster properties ensures good agreement between calculated and measured results and provides a basis for adequate description of the mechanisms of molecular cluster formation in supersonic jets issuing from sonic nozzles characterized by extremely rapid decrease in gas temperature and highly nonequilibrium distribution of energy over molecular degrees of freedom.

Surface induced ionization of neutral water clusters

The paper presents the results of study of a new phenomenon — the formation of cluster ions of both signs in the scattering of neutral water clusters by solid surfaces and the appearance of a current to the target. The experiments were carried out by the nozzle molecular beam technique. The probabilities of the charge removal from the surface were measured in dependence on incident angle, cluster size, and target material. The model of the process has been proposed which incorporates 1) formation of an ion pair during ion dissociation of a vibrationally excited molecule in a water cluster colliding with the surface; 2) asymmetric neutralization of an ion pair by surface; 3) inertial removal of a cluster ion from the surface. However the measured angular and energy distribution of emitted charged particles testify to more complex mechanisms of ionization and scattering because the spatial pattern of ion emission is of rainbow character and in some cases the direction of inertial removal (along the tangential component of initial velocity) does not dominate.

Conversion of municipal sewage sludge in supercritical water

The conversion of the organic matter of municipal sewage sludge in water under supercritical conditions (T≤750°C; P≤30 MPa) was studied. According to mass-spectrometric data, CO2, H2, CH4, and NH3 were predominant among volatile conversion products. The kinetic parameters of conversion were determined. It was found that the rate of the process increased with temperature and mainly depended on the interaction of water molecules with sewage sludge carbon T > 600°C.

The effect of thermal explosion in a supercritical water

The conversion of hydrocarbons (eicosane, naphthalene, and synthetic bitumen) dissolved in super-critical water (SCW) was studied in a batch reactor at a pressure of P=30 MPa and a range of temperatures from 450 to 75°C. It was established that water participates in the conversion process on a chemical level: in particular, oxygen from water molecules is involved in the formation of carbon oxides. Even in the absence of added molecular oxygen, the process of naphthalene and bitumen conversion in a certain temperature interval exhibited an exothermal character. Upon adding O2 into SCW, the oxidation reaction may proceed in a burning regime with self-heating of the mixture. Under certain conditions, the self-heating process may lead to the thermal explosion effect accompanied by ejection of the substance from the reactor, which is explained by the high rate of hydrocarbon burning in SCW.

Cluster generation in expansions of pure water vapour and of mixtures with carbon dioxide

The condensation of pure superheated water vapour and of a mixture with carbon dioxide in a supersonic jet behind a sonic nozzle has been investigated by the nozzle molecular beam method. The relation of source temperature, pressure, and nozzle diameter necessary for fully developed condensation has been determined for the pure vapour. By using the retarding potential technique, the cluster size distribution function and the dependence of the mean cluster size on the nozzle source conditions have been obtained. Mass-spectrometric measurements of the beam composition in a mixture expansion have revealed the presence of both homogeneous and heterogeneous clusters. The fully developed condensation in CO2-H2O mixture was found to begin at a smaller total source pressure than in pure water vapour or carbon dioxide.

Coal gasification with water under supercritical conditions

The conversion of an array of coal particles in supercritical water (SCW) was studied in a semibatch reactor at a pressure of 30 MPa, 500–750°C, and a reaction time of 1–12 min. The bulk conversion, surface conversion, and random pore models were used to describe the conversion. The quantitative composition of reaction products was determined, and the dependence of the rate of reaction on the degree of coal conversion, reaction time, and reaction temperature was obtained on the assumption of a first-order reaction and the Arrhenius function (E = 103 kJ/mol; A0 = 7.7 × 104 min−1). It was found that the gasification of coal under SCW conditions without the addition of oxidizing agents is a weakly endothermic process. The addition of CO2 to SCW decreased the rate of conversion and increased the yield of CO. It was found that, at a 90% conversion of the organic matter of coal (OMC) in a flow of SCW in a time of 2 min, the process power was 26 W/g per gram of OMC.

Naphthalene oxidation in supercritical water

Characteristic features of naphthalene oxidation and the kinetics of naphthalene pyrolysis in supercritical water (SCW) were studied using a batch reactor under isobaric conditions at a pressure of 30 MPa, in the temperature range from 660 °C to 750 °C, and for different levels of oxygen supply, varying from 0 to 2.5 moles of O2 per mole of naphthalene. The pyrolysis produces benzene, toluene, methane, hydrogen, soot, and carbon oxides. The rate constant for naphthalene pyrolysis in SCW was found to be k = 1012.3±0.2exp(–E/T) s–1 where E = 35400±500 K. For T > 660 °C, water participates in the chemical reactions of naphthalene conversion, particularly, in the formation of carbon oxides. The conversion of naphthalene in pure SCW is accompanied by heat evolution. Molecular oxygen oxidizes a part of naphthalene completely, i.e., to CO2 and H2O, this reaction being so prompt that in some cases, self-heating of the mixture and thermal explosion in the reactor were observed.

Absolute cross sections of electron attachment to molecular clusters. Part II: Formation of (H2O)-N, (N2O)-N, and (N2)-N

Absolute cross sections σ−(E, N) of electron attachment to clusters (H2O)N, (N2O)N, and (N2)N for varying electron energy E and cluster size N are measured by using crossed electron and cluster beams in a vacuum. Continua of σ−(E) are found that correlate well with the functions of electron impact excitation of molecules’ internal degrees of freedom. The electron is attached through its solvation in a cluster. In the formation of (H2O)N−, (N2O)N−, and (N2)N−, the curves σ−(N) have a well-defined threshold because of a rise in the electron thermalization and solvation probability with N. For (H2O)900, (N2O)350, and (N2)260 clusters at E = 0.2 eV, the energy losses by the slow electron in the cluster are estimated as 3.0 × 107, 2.7 × 107, and 6.0 × 105 eV/m, respectively. It is found that the growth of σ− with N is the fastest for (H2O)N and (N2)N clusters at E → 0 as a result of polarization capture of the s-electron. Specifically, at E = 0.1 eV and N = 260, σ− = 3.0 × 10−13 cm2 for H2O clusters, 8.0 × 10−14 cm2 for N2O clusters, and 1.4 × 10−15 cm2 for N2 clusters; at E = 11 eV, σ− = 9.0 × 10−16 cm2 for (H2O)200 clusters, 2.4 × 10−14 cm2 for (N2O)350 clusters, and 5.0 × 10−17 cm2 for (N2)260 clusters; finally, at E = 30 eV, σ− = 3.6 × 10−17 cm2 for (N2O)10 clusters and 3.0 × 10−17 cm2 for (N2)125 clusters.

Electron-induced radiation from C60 fullerene in the gas phase

The formation of radiating particles in the excitation of C60 fullerene molecules by electrons with energies Ee<100 eV is investigated by the method of crossed molecular and electron beams. A quasicontinuous (with a spectral resolution of 3 nm) emission spectrum, close to the Planck emission spectrum of a heated body, is recorded in the wavelength range 300–800 nm. The temperature of the radiation corresponds to an internal energy of the C60 molecule of approximately 40 eV.