Ar Molecules Research Articles

Gas Adsorption Studies of Ar Molecules on a High-Energy-BeamIrradiated MgO Surface

Gas adsorption studies are useful to investigate the ne structure of a surface on an atomic scale. A meso-sized MgO (100) powder surface prepared by using the RF-induction method was irradiated by using an electron beam with energy of 2 MeV. The amount of electron beam dosage was varied from 20 kGy to 1000 kGy. By measuring the Ar gas adsorption data recorded below the triple point (83.78 K), we analyzed the surface changes in the MgO powder before and after the electron beam irradiation. X-ray and TEM investigations revealed that the surface structure was not a ected by the irradiation with an electron beam. Calculated values of the 2-dimensional compressibility and the isosteric heat of adsorption coherently showed that a stronger interaction of Ar molecules existed for the electron-irradiated MgO powders than for the pure samples. These results imply the possibility of local surface modi cation due to bombardments with external electrons.

A cryogenic supersonic nozzle apparatus to study homogeneous nucleation of Ar and other simple molecules

We present a supersonic nozzle apparatus to study homogeneous nucleation of argon and other simple molecules. Experiments can be conducted with pure condensable vapor or with condensable vapor-carrier gas mixtures. The flow through the nozzle is continuous, and expansions typically start at temperatures T(0) in the range of 100<T(0)/K<120, and pressures p(0) in the range of 30<p(0)/kPa<36. The gas mixture is cooled using a tube and fin heat exchanger by evaporating liquid nitrogen on the tube side. The nozzle sidewalls are also cooled with liquid nitrogen to maintain them at a temperature approximately 20 K higher than the stagnation temperature. Static pressure measurements detect the onset of condensation, and the other properties of the flow are derived by integrating the diabatic flow equations. We present sample experimental results for pure argon where at the onset of condensation, temperatures T(on) range from 47.5<T(on)/K<49.5 and pressures p(on) range from 4.2<p(on)/kPa<4.9.

Clustering Dynamics of the Metal−Benzene Sandwich Complex: The Role of Microscopic Structure of the Solute In the Bis(η6-benzene)chromium ·Arn Clusters (n = 1−15)

Ar clustering dynamics around the metal-benzene sandwich complex, bis(eta (6)-benzene)chromium: Cr(Bz) 2, is found to occur in two distinct regimes. The shift of the ionization potential (IP) upon the addition of Ar is measured to be 151 cm (-1), and it is constant until the number of Ar solvents ( n) becomes 6. The IP shift per Ar is found to be suddenly decreased to 82 cm (-1) for the clusters of n = 7-12. The cluster distribution indicates that the n = 6 cluster is most populated in the molecular beam. These experimental findings with the aid of ab initio calculation indicate that the first six Ar solvent molecules are attached to top and bottom of Cr(Bz) 2 to give the robust structure for the Cr(Bz) 2-Ar 6 cluster whereas the next six Ar molecules are gathered on the side of the solute core to give the highly symmetric structure of the Cr(Bz) 2-Ar 12 cluster.

Effect of active impurities on the condensation of nanoparticles from supersaturated carbon vapor in the combined laser photolysis of C3O2 and H2S

The effect of active H2S, HS·, and atomic hydrogen impurities on the condensation of highly supersaturated carbon vapor obtained in the combined laser photolysis of a mixture of C3O2 and H2S diluted with argon was studied. The concentrations of carbon vapor, HS·, and atomic hydrogen obtained in the laser photolysis of the mixture were determined using the absorption cross sections of C3O2 and H2S molecules measured in this work and the measured amount of absorbed laser radiation. The time profiles of the sizes of growing nanoparticles synthesized in C3O2 + Ar and C3O2 + H2S + Ar mixtures were measured using the laser-induced incandescence (LII) method. An improved LII model was developed, which simultaneously took into account the heating and cooling of nanoparticles and the temperature dependence of the thermophysical properties of nanoparticles, as well as the cooling of nanoparticles by evaporation and thermal emission. The size distributions of carbon nanoparticles formed in the presence and absence of active impurities were determined with the use of a transmission electron microscope. The final average size of carbon nanoparticles was found to decrease from 12 to 9 nm upon the addition of H2S to the system, whereas the rate of nanoparticle growth decreased by a factor of 3, and the properties of nanoparticles changed. In particular, the translational energy accommodation coefficient for Ar molecules at the surface of carbon nanoparticles was found to decrease from 0.44 to 0.30. A comparison of the calculated total carbon balance at the early stage of nanoparticle formation with experimental data demonstrated that the reaction C + H2S → HCS· + H, which removes a portion of carbon vapor from the condensation process, has a determining effect on the carbon balance in the system. It was found that HS· and atomic hydrogen affect the carbon balance in the system only slightly. Thus, the experimentally observed decrease in the rate of nanoparticle growth and in the sizes of nanoparticles can be explained by a decrease in the concentration of free carbon upon the addition of H2S molecules to the system.

Real-time multielement monitoring of airborne particulate matter using ICP-MS instrument equipped with gas converter apparatus

The real-time multielement monitoring of airborne particulate matter (APM) was carried out using an inductively coupled plasma mass spectrometry (ICP-MS) instrument equipped with a newly developed gas converter apparatus. By using the gas converter apparatus, gas molecules in the air sample and Ar molecules were almost completely exchanged and the gas-converted air sample could be directly introduced into ICP-MS instruments. Fe in clean room and outdoor air samples was directly measured using the ICP-MS instrument equipped with the converter apparatus. The signal intensities of Be, Ag, Cd, Sn, Sb, Tl, Pb, Bi, Th, and U in the outdoor air sample were successfully measured at every 8 min for 77 h.

Stochastic Perturbation Theory: A Low-Scaling Approach to Correlated Electronic Energies

We discuss a stochastic implementation of Møller-Plesset (MP) theory based upon the concept of a "graph," a set of connected Slater determinants. We show how contributions from an arbitrary level, MPn, of perturbation theory can be expressed diagrammatically in terms of graphs, and that these may be stochastically sampled to give a good estimate of the energy. We show this to be the case for Ne, Ar, N2, and H2O molecules. N-molecule chains of He atoms and H2 molecules at equilibrium and stretched geometries show an effective scaling of O[N(2.6)] and O[N(5.6)] for MP2 and MP3 theories.

Dynamic Behaviors of a&lt;sub&gt;1B&lt;/sub&gt;-Adrenergic Receptor in Living Cells

AIM: The present study aims at investigating dynamic behaviors of a 1B -adrenergic receptor (a 1B -AR) at molecular level in living cells. METHODS: Wide-field imaging was applied on the detection of real-time dynamic behaviors of a 1B -AR using fluorescence-labeled prazosin (Praz), a specific antagonist of α 1 -AR, in a 1B -AR stably expressed human embryonic kidney 293 (HEK293) living cells. The precise localization around 10 nanometers with 2D Gaussian function was applied in the analysis of the trajectory of molecular movement. RESULTS: The specific binding characteristic of BODIPY-Praz in living cells was identified by the real-time observation that phentolamine competitively inhibits the BODIPY-Praz binding to the receptor at a molecular level in HEK293 living cell. The directional and trapped motions of a 1B -AR molecules in living cells were observed and analyzed at millisecond time resolution and nanometer space resolution. The speeds of the two typical motions were distributed in two different scopes with the peak value of 1.08 and 0.55 μm/s, respectively. The directed motions in living cells were obviously diminished by the previous incubation with the microtubule disrupting agent nocodazole. CONCLUSION: a 1B -AR with binding function was visualized by BODIPY-labeled Praz at molecular level in living cells. The directed and trapped motions have the different speed distributions in living cells. The directed motion of a 1B -AR in living cells might be walking along microtubules.

Formation of carbon nanoparticles by the condensation of supersaturated atomic vapor obtained by the laser photolysis of C3O2

A new technique is suggested for obtaining nanoparticles from highly supersaturated vapor resulting from the laser photolysis of volatile compounds. The growth of carbon nanoparticles resulting from C3O2 photolysis has been studied in detail. Absorbing UV quanta (from an Ar-F excimer laser), C3O2 molecules decompose to yield atomic carbon vapor with precisely known and readily controllable parameters. This is followed by the condensation of supersaturated carbon vapor and the formation of carbon nanoparticles. These processes have been investigated by the laser extinction and laser-induced incandescence (LII) methods in wide ranges of experimental conditions (carbon vapor concentration, nature of the diluent gas, and gas pressure). The current and ultimate particle sizes and the kinetic parameters of particle growth have been determined. The characteristic time of particle growth ranges between 20 and 1000 μs, depending on photolysis conditions. The ultimate particle size determined by electron microscopy is 5–12 nm for all experimental conditions. It increases with increasing total gas pressure and carbon vapor partial pressure and depends on the diluent gas. The translational energy accommodation coefficients for the Ar, He, CO, and C3O2 molecules interacting with the carbon particle surface have been determined by comparing the LII and electron microscopic particle sizes. A simple model has been constructed to describe the condensation of carbon nanoparticles from supersaturated atomic vapor. According to this model, the main process in nanoparticle formation is surface growth through the addition of separate atoms to the nucleation cluster. The nucleus concentrations for various condensation parameters have been determined by comparing experimental and calculated data.

TR-LII for sizing of carbon particles forming at room temperature

Time-resolved laser-induced incandescence (TR-LII) was applied for the determination of particle sizes during carbon-particle formation from supersaturated atomic carbon vapor that was generated by laser photolysis of carbon suboxide (C3O2) at room temperature. Thus, the solid carbon particles were formed under hydrogen-free conditions. The TR-LII technique was used for in situ size measurement of growing carbon particles and samples of final particles were analyzed by transmission electron microscopy (TEM). It was found that the particles grow to a final size of 4–12 nm within 0.02–1 ms. The properties of the obtained particles depend on the initial conditions in the reaction volume, i.e. concentration of carbon suboxide, pressure and type of gas diluter, photolysis wavelength, and laser pulse energy. The comparison of TR-LII and TEM particle sizing results yields information about the effective thermal energy accommodation coefficients for He, Ar, CO, and C3O2 molecules on carbon particles.

Effect of Surface Resistances on the Diffusion of Binary Mixtures in the Silicalite Single Crystal Membrane

Diffusion of methane and argon mixtures through the silicalite single-crystal membrane is studied using the dual-control volume-grand canonical molecular dynamics method to understand how surface resistances alter selectivity and permeance. Comparison of results from intracrystalline transport and entrance simulations for binary mixtures of CH4 and Ar shows that the selectivity of silicalite membranes toward Ar is enhanced in the presence of the surface resistances. In both cases, however, diffusion of faster Ar molecules was inhibited by slower diffusing CH4 molecules, whereas diffusion of the latter remained unaffected. This behavior was explained by the difference between the magnitudes of surface resistances for two molecules, which is much smaller for Ar because of its smaller permeant-crystal interaction size. We find that selectivity of the membrane at the surface depends strongly on total feed pressure and temperature, whereas this dependence is weak for intracrystalline diffusion. Furthermore, we show that the selectivity at the surface diminishes with crystal thickness until a certain thickness is reached, whereas the intracrystalline selectivity remains constant with increasing thickness. Finally, a study of diffusion of C2H6 and CF4 mixtures shows that the diatomic ethane molecules diffuse faster inside the zeolite channels, but their desorption is hindered to a larger extent than that of a spherical molecule with larger diameter and lower heat of adsorption. This observation indicates that the difference in molecular geometry is also a significant factor to explain the exit effect.

The nature of the Au–Rg bond in the [AuRg4]2+ (Rg=Ar, Kr and Xe) molecules

A topological analysis of the electron localisation function of the [AuRg4]2+ (Rg = Ar, Kr and Xe) molecules reveals the `closed-shell' nature of the Au–Rg binding, which is dominated by electrostatic interactions. A similar finding is obtained by means of the AIM method where the Laplacian of the electron density computed for the bond critical point of the Au–Rg linkage is positive and decreases from 0.163 [AuAr4]2+ to 0.087 [AuXe4]2+. A charge separation according to the Au+1.30[Ar+0.18]4, Au+1.19[Kr+0.20]4 and Au+0.29[Xe+0.43]4 formulas shows an increase of the positive charge on the rare-gas atom and accordingly decrease on the gold atom. The unpaired electron density is localised mainly on Au and the integrated spin density decreases from 0.28 e for [AuAr4]2+ to 0.16 e for [AuXe4]2+.

1514 金属表面酸化加熱過程の分子スケール解析

Oxidation and heating processes of Ag surface are simulated using the molecular dynamics method in order to analyze adsorptive probability and energy transfer of O_2 molecule to Ag surface. We have investigated effects of surface temperature and adherent molecules, such as Ar, Kr and Xe molecules on reaction probability and energy transfer to Ag surface in molecular scale Reaction probability of O_2 molecules is much different depending on kinds of adherent molecules on Ag surface. Dynamic behaviors of adherent molecules on Ag surface affect reaction probability substantially when translation energy of O_2 molecules is relatively small. Energy transfer from O_2 molecule to Ag surface is also dependent on physical properties and dynamic behaviors of adherent molecules.

Affect on pumping-speed measurements due to variations of test dome design based on Monte Carlo analysis

Test domes for measuring the pumping speed of cryopumps are defined in Pneurop standard PN5ASRCC/5 and the American Vacuum Society Recommended Practice for Cryopumps published in 1999. The test domes try to provide a measure of the speed of a pump as if the cryopump is mounted in the center of a large flat plate in a large chamber. This is referred to as the intrinsic speed. In this case, the flow distribution into the pump is diffuse while in the test dome the flow pattern has a stronger axial component. The location of the pressure gauge is intended to compensate for the different flow pattern. Certain parameters in the design of the test domes are not rigidly specified. A Monte Carlo analysis (MCA) has been carried out to analyze the differences in speed that will be measured for different allowable configurations of the test dome. The results show that the variations that are allowed in the recommended practice have little impact on differences in the pumping speed that will be measured. The analysis shows that the axial flow is greater and more uniform in the two-gauge dome than the single dome. The different flow patterns have no impact on pumps that have “porous” inlets (uniform capture probability from all angles) and the recommended location of the pressure gauge gives measured speeds that are very close to the intrinsic speed. Pumping speed measurements of a real cryopump are influenced by the flow pattern. The APD Cryogenics M8 cryopump was analyzed using MCA and found to have calculated speeds that are about 9% higher than the intrinsic speed in the single dome and 11% higher in the two-gauge dome. The probability of Ar molecules being captured by an M8 cryopump in either test dome is about 11% greater than in a large chamber.

Effect of low temperature adsorption of N2, O2 and Ar on superconductivity of GdBa2Cu3O7-x films

By measuring the imaginary part of the magnetic susceptibility of a GdBa2Cu3O7-x film, we found the effect of N2, O2 and Ar molecules low temperature adsorption on the superconducting properties of the film. The low temperature adsorption of the gases affects the critical transport current and the transition temperature. In all cases, the transition region broadens, as the degree of coverage of the film with the gas molecules increases. By processing the experimental data, we found the critical current either growing linearly (for argon and nitrogen) or decreasing exponentially (for oxygen) with increasing surface coverage by the adsorbed gas molecules.

Solvent isotope effects on the solubility of argon and pair interactions in aqueous solution of hexamethylenetetramine

The solubilities of gaseous argon in solutions of hexamethylenetetramine (hmta) in H2O and D2O were measured at different concentrations, at five temperatures in the range of 283–318 K, and at a partial gas pressure of 101325 Pa by microvolumetry with an accuracy of ≤0.3%. The standard Setchenov coefficients for argon solutions and the thermodynamic parameters of Ar-hmta pairwise interactions were calculated from the data on the solubility. Interactions between hydrated Ar and hmta molecules are characterized by mutual repulsions. The structural states of water in the hydration sphere of hmta and in the bulk of solution are substantially different. Due to the difference in the mechanisms of hydration of hmta and Ar, the addition of the first component leads to a decrease in the solubility of the second component.

Spectroscopy of Neurotransmitters and Their Clusters: Phenethylamine and Amphetamine Solvation by Nonpolar, Polar, and Hydrogen-Bonding Solvents

Clusters containing a phenylethylamine (PEA) or amphetamine (AMP) molecule and a solvent species such as Ar, CH4, CF3H, CO2, H2O, and other small molecules are formed in a supersonic jet expansion. Spectral studies of the solvation and related chemistry of PEA and AMP are pursued by using both fluorescence and mass spectroscopy techniques. To help analyze the experimental results, ab initio and atom−atom Lennard-Jones−Coulomb (LJC) potential calculations are employed to calculate cluster geometries and binding energies. The LJC potential parameters for the 10−12 hydrogen-bonding potentials have been reevaluated on the basis of new ab initio partial atomic charge values and new experimental binding energies and geometries. The observed dependence of the relative spectral intensities of PEA and AMP conformers and their clusters on the cooling conditions (backing pressure and coolants employed) suggests that these species undergo population redistribution in the cooling and clustering process. The amount of excess energy (binding energy) available to the forming cluster plays a major role in the conformational conversion of PEA and AMP during cluster formation. If strong interactions (hydrogen bonding) exist between the solute and the solvent, such conversion/redistribution processes occur among all conformers and their clusters. The conversion/redistribution process is restricted within the anti or gauche conformer sets and their clusters for weakly interacting solute/solvent pairs. All PEA and AMP clusters studied experience complete fragmentation upon ionization. The observed gradual dependence of photo ion intensity on the ionization laser energy suggests a significant change in geometry for both PEA and AMP, as well as their clusters, upon ionization. Consequently the high vertical ionization energy leads to an excess energy in the vibrational modes of the ions, causing fragmentation of the clusters. The clusters can fragment along two different general paths: (1) simple loss of the solvent molecules and (2) breaking the α−β carbon bond of PEA or AMP, with additional loss of solvent molecules in some cases. Those clusters with weaker solute/solvent binding tend to fragment through solvent loss, while those forming hydrogen bonds tend to favor the α−β carbon bond cleavage. Reactions are observed for PEA and AMP with NO. NO can completely quench PEA and AMP monomer spectra. The reaction products include C6H5CHCH2 and C6H5NH2 for PEA and C6H5CHCHCH3 and C6H5NH2 for AMP.

Detection of beta 2-adrenergic receptor dimerization in living cells using bioluminescence resonance energy transfer (BRET)

Heptahelical receptors that interact with heterotrimeric G proteins represent the largest family of proteins involved in signal transduction across biological membranes. Although these receptors generally were believed to be monomeric entities, a growing body of evidence suggests that they may form functionally relevant dimers. However, a definitive demonstration of the existence of G protein-coupled receptor (GPCR) dimers at the surface of living cells is still lacking. Here, using bioluminescence resonance energy transfer (BRET), as a protein-protein interaction assay in whole cells, we unambiguously demonstrate that the human beta(2)-adrenergic receptor (beta(2)AR) forms constitutive homodimers when expressed in HEK-293 cells. Receptor stimulation with the hydrophilic agonist isoproterenol led to an increase in the transfer of energy between beta(2)AR molecules genetically fused to the BRET donor (Renilla luciferase) and acceptor (green fluorescent protein), respectively, indicating that the agonist interacts with receptor dimers at the cell surface. Inhibition of receptor internalization did not prevent agonist-promoted BRET, demonstrating that it did not result from clustering of receptors within endosomes. The notion that receptor dimers exist at the cell surface was confirmed further by the observation that BS3, a cell-impermeable cross-linking agent, increased BRET between beta(2)AR molecules. The selectivity of the constitutive interaction was documented by demonstrating that no BRET occurred between the beta(2)AR and two other unrelated GPCR. In contrast, the well characterized agonist-dependent interaction between the beta(2)AR and the regulatory protein beta-arrestin could be monitored by BRET. Taken together, the data demonstrate that GPCR exist as functional dimers in vivo and that BRET-based assays can be used to study both constitutive and hormone-promoted selective protein-protein interactions.

Collisional Relaxation of Highly Vibrationally Excitedcis-ClFCCFCl Prepared by Multiphoton Excitation

Highly vibrationally excited gas-phase cis-ClFCCFCl was prepared with a pulsed, high-powered pulsed TEA CO2 laser operating at 948 cm-1, and the subsequent collisional relaxation was followed by infrared fluorescence from the ν2 mode (1168 cm-1). Energy transfer data were obtained for Ar and ClFCCFCl molecules as collisional partners. The exponential decay of the average energy together with the linear microcanonical dependence of I(E) on 〈E〉 in a wide energy range allowed for the determination of the dependence of bulk average energy transfer per collision, 〈〈ΔE〉〉, on the average energy, 〈〈E〉〉. In both cases, 〈〈ΔE〉〉 is found to be a linear function of 〈〈E〉〉. As the energy decay profiles are exponential, they are independent of the shape of the initial distribution and of the fraction of molecules excited, allowing one to obtain the dependence of the microscopic first moment of P(E‘,E), 〈ΔE〉, on 〈E〉. The following dependences of 〈ΔE〉 on 〈E〉 were found:〈ΔE〉P = 4.5 ± 1.0 − (7.3 ± 1.5) × 10-3〈E〉 cm-1 for sel...

On the à and B̃ electronic states of NCO and its clusters with nonpolar solvents

The B̃←X̃ and Ã←X̃ transitions of the NCO radical and its clusters with nonpolar solvents are studied in a supersonic jet expansion by employing laser-induced fluorescence techniques. Fluorescence excitation (FE) and hole burning spectra are recorded for the NCO radical and compared to previous work. NCO is clustered with Ar, N2, CH4, and CF4 nonpolar molecules to elucidate the effect of solvation on the radical energy levels and dynamics. FE spectra are detected for NCO 1:1 clusters showing blue shifts in their spectra with respect to that of the isolated NCO radical, while their 1:n counterparts show either red or blue shifts. Potential energy surface calculations are performed to evaluate the binding energies and geometries of 1:1 clusters in the X̃, Ã, and B̃ electronic states. The relatively long decay lifetime and red shifted fluorescence wavelength range observed for B̃ state clusters suggests that they decay first through internal conversion (IC) to à vibronic levels, and then experience rapid intracluster vibrational redistribution (IVR) and vibrational predissociation (VP), yielding ground state solvent molecules and NCO radicals at lower à vibronic levels. These à state NCO radicals subsequently emit, generating the Ã→X̃ band.

The 3d←3p endothermic collisional population transfer of Li in He and Ar at 298 K

The 3p state of Li was excited in He and Ar buffer gases at room temperature (298 K) and the time profiles of sensitized fluorescence from the 3s and 3d states were measured. The 3d←3p endothermic population transfer rates determined from the pressure dependence of the time profiles were 6.5×10 −11 cm 3 s −1 for He and less than 10 −3 cm 3 s −1 for Ar. The origin of this large difference between He and Ar is discussed in terms of non-adiabatic transitions between the 3p and 3d molecular states of the Li–He and Li–Ar molecules.