Molecular Beam Velocity Research Articles

Influence of injection parameters on fueling efficiency of supersonic molecular beam injection into turbulent fusion plasmas

The fueling efficiency of supersonic molecular beam injection (SMBI) depends on injection parameters. In this article, we report on simulations of SMBI into turbulent edge fusion plasmas. Density continuity equations, which describe the dynamics of molecules and Franck-Condon atoms, are coupled with the plasma equations in the hot-edge-sol-electrostatic (HESEL) drift-fluid model. Numerical simulations, with parameters relevant to experimental conditions, are performed in order to investigate the dependency of the fueling efficiency of SMBI on the molecular beam density, velocity, and beam width. In all conditions, the efficiency grows with the increase in the molecular beam velocity. The variation in efficiency with respect to the beam density depends on the plasma pressure and the ratio of the density source, produced by ionization of neutrals, to the plasma density source provided by core fueling. The effect of the molecular beam width is pronounced only if the beam density is high and the plasma, into which the beam is injected, is relatively dense and hot. The influence of plasma fluctuations on SMBI is weak; however, a strong neutral injection leads to suppression of a turbulence transport due to relaxation of pressure gradient profiles.

Deceleration of continuous molecular beams

A method for decelerating a continuous beam of neutral polar molecules is theoretically demonstrated. This method utilizes non-uniform, static electric fields and regions of adiabatic population transfer to generate a mechanical force that opposes the molecular beam's velocity. By coupling this technique with dissipative trap-loading, molecular densities $\geq10^{11}$ cm$^{-3}$ are possible. When used in combination with forced evaporative cooling the proposed method may represent a viable route to quantum degeneracy for a wide-class of molecular species.

Slow Molecules Produced by Photodissociation

A simple method to control molecular translation with a chemical reaction is demonstrated. Slow NO molecules have been produced by partially canceling the molecular beam velocity of NO 2 with the recoil velocity of the NO photofragment. The NO 2 molecules were photodissociated using a UV laser pulse polarized parallel to the molecular beam. The spatial profiles of NO molecules showed two peaks corresponding to decelerated and accelerated molecules, in agreement with theoretical prediction. A significant portion of the decelerated NO molecules stayed around the initial dissociation positions even several hundred nanoseconds after their production.

Controlling the motion of cold molecules with deep periodic optical potentials

The application of optical forces has allowed unprecedented control over the motion of atoms leading to laser cooling and trapping1 and Bose–Einstein condensation2. More recently, the manipulation of cold neutral polar molecules using electrostatic fields has been used to create slow cold molecules in the laboratory frame3. Here, we report on the controlled manipulation of molecules using deep periodic optical lattice potentials (22 K) created by intense optical fields (1011 W cm−2). By using the oscillatory motion of nitric oxide molecules in these potentials, we have demonstrated rapid deceleration or acceleration in a molecular beam to well-defined velocities on a length scale of less than 535 nm. We reduce the kinetic energy of the molecules in a cold molecular beam by up to 50% in a single laser pulse (5.8 ns) demonstrating precise control of molecular-beam velocity and a new method for creating slow cold molecules using optical fields.

New insights on the stereodynamics of ethylene adsorption on an oxygen-precovered silver surface

The control of spatial orientation of molecules has a great influence on the stereodynamics of elementary processes occurring both in homogeneous and heterogeneous phases. Nonpolar molecules have so far escaped direct experimental investigations because of their poor sensitivity to several external constraints. Recently, it has been shown that the collisional alignment produced in supersonic expansions coupled with molecular-beam velocity selection can help solve such problems. Here we show that the sticking probability of ethylene, a nonpolar molecule prototypical of unsaturated hydrocarbons, on an O(2)-precovered Ag(001) surface is larger for molecules approaching in a helicopter-like motion than for those cartwheeling. A mechanism involving a weakly bound precursor state is suggested, with helicopter molecules having a lower chance of being scattered back into the gas phase than cartwheels when colliding with preadsorbed ethylene.

Imaging the quantum-state specific differential cross sections of HCl formed from reactions of chlorine atoms with methanol and dimethyl ether.

Center-of-mass frame scattering angle distributions obtained directly from crossed molecular beam velocity map images are reported for HCl formed in different rotational levels of its vibrational ground state by reaction of Cl atoms with CH3OH and CH3OCH3. Products are observed to scatter over all angles, with peaks in the distribution in the forward and backward directions (theta = 0 and 180 degrees with respect to the relative velocity vectors of the Cl atoms). Products of both reactions exhibit differential cross sections that vary with the rotational quantum number of the HCl, with a greater propensity for forward scatter for J = 2, shifting to more pronounced backward scatter for J = 5. This trend is, however, more evident for reaction of dimethyl ether than for methanol. The mean fractions of the available energy channeled into product kinetic energy vary with scattering angle, but the angle-averaged fractions are, respectively, 0.37 and 0.42 for the methanol and dimethyl ether reactions. On average, 46% or more of the available energy of the reactions becomes internal energy of the radical co-product. Results are interpreted with the aid of computed energies of transition states and molecular complexes along the reaction pathways, and comparisons are drawn with recent measurements of the scattering distributions and energy release for reactions of Cl atoms with small alkanes.

State-to-state cross sections for rotational excitation of ortho- and para-NH 3 by Ar

Parity resolved state-to-state cross sections for rotational and tunneling inversion excitation of ortho- and para-NH 3 colliding with Ar, have been obtained in a crossed molecular beam experiment. State preparation of the 0 + 0 state for ortho-NH 3 and the 1 − 1 state for para-NH 3 is achieved by adiabatic expansion of ammonia followed by electrostatic state selection in a hexapole electric field. The NH 3 rotational state distribution is probed by (2 + 1) REMPI spectroscopy via the B state. The scattering experiments have been performed at two collision energies, 35 meV and 56 meV, by varying the NH 3 molecular beam velocity. The experimental values for the relative cross sections are compared with the results from close coupling calculations using an ab initio potential. Also a modified potential scaled to spectroscopic data for the NH 3-Ar complex is considered. For ortho-NH 3 observed parity propensities are in good agreement with theoretical predictions. In the case of para-NH 3 discrepancies are present. For the parity averaged rotational excitation a reasonably good agreement between experiment and theory is obtained.

Auger-electron spectra formation under solid surface bombardment by diatomic molecular beams

The calculation of the characteristic Auger-electron spectrum, emitted under solid surface bombardment by accelerated diatomic molecular ion beams, has been performed. Non-additivity of such spectra, realized in both the shift and broadening of the characteristic peak, observed under monoatomic ion bombardment has been exhibited. The shift and broadening values have been shown to be defined by three parameters: the molecular beam velocity, the corresponding vacancy lifetime and the screening parameter. The possibility of the relative contribution estimation of symmetrical and asymmetrical collisions into the given peak formation has been discussed. In addition the connection between the proton charge state inside the metal and the characteristics of Auger-electron spectra, observed under molecular beam bombardment, have been considered.

Energy accommodation and reactivity of O2 on tungsten

We have determined by direct molecular beam velocity measurements that translational energy accommodation of O2 molecules scattered from a hot polycrystalline tungsten target is inefficient at high surface temperatures. Translational energy accommodation is inefficient whether the surface is clean or covered with oxygen to a varying extent, even though in the latter case the scattering is diffuse. On a clean tungsten surface the scattering of the O2 was approximately specular and the reaction probability of O2 was constant and greater than 90% over the temperature range 1000K to 2800 K. It was shown by simultaneous helium scattering that atomic surface roughness of an oxygen chemilayer, rather than trapping, is a major cause of the observed diffuse scattering of oxygen. At the lowest surface temperature of 1000 K, with an oxygen chemilayer present, the velocity of the most probable number density of the scattered O2 was lower than in the incoming beam or than that expected for complete equilibration with the surface.

ChemInform Abstract: STUDY OF BORANE PRODUCTION FROM PYROLYZED DIBORANE BY MOLECULAR BEAM VELOCITY ANALYSIS SPECTROMETRY

Chemischer InformationsdienstVolume 8, Issue 17 Preparative Inorganic Chemistry ChemInform Abstract: STUDY OF BORANE PRODUCTION FROM PYROLYZED DIBORANE BY MOLECULAR BEAM VELOCITY ANALYSIS SPECTROMETRY B. S. ASKINS, B. S. ASKINSSearch for more papers by this authorC. RILEY, C. RILEYSearch for more papers by this author B. S. ASKINS, B. S. ASKINSSearch for more papers by this authorC. RILEY, C. RILEYSearch for more papers by this author First published: April 26, 1977 https://doi.org/10.1002/chin.197717027Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume8, Issue17April 26, 1977 RelatedInformation

Study of borane production from pyrolyzed diborane by molecular beam velocity analysis spectrometry

Study of borane production from pyrolyzed diborane by molecular beam velocity analysis spectrometry

New laser-induced fluorescence method for molecular beam velocity analysis

We have measured the velocity distribution of a Na2 supersonic beam by a time of flight method in which a chopped beam from an argon ion laser depopulates a single vibration–rotation level of the Na2 ground electronic state, and a continuous laser beam further downstream is used to detect the arrival of the tagged molecules by observation of changes in the laser-induced fluorescence.

New compact molecular beam velocity selector

A new, compact, molecular beam velocity selector is described. It utilizes the same principle as the slotted disks velocity selectors but consists only of one disk incorporating a series of multichannel collimators. Advantages: simplicity, short length, light weight. Disadvantages: limited resolution and limited maximum speed selected.

Entropy and Chemical Change. II. Analysis of Product Energy Distributions: Temperature and Entropy Deficiency

Detailed experimental and theoretical information on the distribution of product energy states resulting from reactive molecular collisions are characterized by their entropy deficiency and temperature. Explicit algorithms are developed both for the case of ultimate resolution (both angular and internal state distribution) which provides the intrinsic (i.e., maximal) entropy deficiency and for the more realistic situations (e.g., chemiluminescence, molecular beam velocity analysis) where only averaged distributions are available and the entropy deficiency is therefore smaller. Twelve ``known'' product distributions are analyzed. The largest values of the entropy deficiency are found for reactions where there is significant deviation from a simple equilibrium distribution of products. A temperature parameter is introduced as a measure of the deviation from equilibrium. Inverted populations are characterized by a negative value of this temperature. Consideration of a number of isotopic reactions indicate that this temperature is essentially invariant under isotopic substitution. The new temperature parameter introduced in this work is the one appropriate for a finite system and differs from the more familiar (but special) form appropriate for a system coupled to an infinite heat bath. Two new tools are thus proposed for characterizing the deviation of an observed product state distribution (or a computational simulation thereof) from an equilibrium, microcanonical one. These are the temperature parameter (a differential measure) and the entropy deficiency (an integral one). They measure, respectively, the local and the average deviation between observed and equilibrium distributions.

A Molecular Beam Velocity Selector of Easy Construction

A Molecular Beam Velocity Selector of Easy Construction

A Radial Disk Velocity Selector for Molecular Beams

A molecular beam velocity selector is reported in which the beam passes diametrically across a rotating slotted disk. Alignment is checked without reference to assumptions about the source velocity distribution. The selector is compact, easily constructed, and is mounted directly on the driving motor shaft.

Velocity Analysis of Molecular Beams Generated from NaOH Vapors

A molecular beam velocity analysis technique has been employed to determine the molecular composition of vapors in equilibrium with liquid sodium hydroxide in the temperature range 887–996°K. The experimental results are nonreproducible to an extent which far exceeds the expected experimental uncertainties. It is inferred that this anomalous behavior is characteristic of the NaOH system and several possible explanations for the discrepancies are discussed.

Polymeric Gaseous Molecules in the Vaporization of Alkali Halides

The molecular species of alkali halide vapors in equilibrium with their respective condensed phases have been deduced by a mass spectrometric analysis of the ions produced by electron impact. Dimers, trimers, and in some instances tetramers MnXn were observed, with the lithium halides exhibiting more dimeric than monomeric species. The results are in substantial agreement with earlier molecular beam velocity selector experiments, and discordant with some recent infrared spectral studies. Some oddities in the ionization efficiency curves are also discussed.