Cold Chemistry Research Articles

Toward Cold Chemistry with Magnetically Decelerated Supersonic Beams

ADVERTISEMENT RETURN TO ISSUEPREVReviewNEXTToward Cold Chemistry with Magnetically Decelerated Supersonic BeamsEdvardas Narevicius*† and Mark G. Raizen‡View Author Information† Department of Chemical Physics, Weizmann Institute of Science, Rehovot 76100, Israel‡ Center for Nonlinear Dynamics and Department of Physics, The University of Texas at Austin, Austin, Texas 78712, United States *E-mail: [email protected]Cite this: Chem. Rev. 2012, 112, 9, 4879–4889Publication Date (Web):July 24, 2012Publication History Received6 December 2011Published online24 July 2012Published inissue 12 September 2012https://doi.org/10.1021/cr2004597Copyright © 2012 American Chemical SocietyRIGHTS & PERMISSIONSArticle Views2012Altmetric-Citations71LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit Read OnlinePDF (7 MB) Get e-AlertsSUBJECTS:Cancer,Hydrogen,Kinetics,Magnetic properties,Molecules Get e-Alerts

Prediction of coke quality using adaptive neurofuzzy inference system

The production rate, quality and cost of hot metal production through the blast furnace route depend mainly on the quality of the metallurgical coke. Coke reactivity index and coke strength after reaction (CSR) are the most important parameters used for the assessment of the high temperature properties of coke. Many coke plants and blast furnaces around the world use CSR as a specification just as important as cold strength, size and chemistry. The present work aims to fulfil the need for a model that will predict the coke CSR from coal blend characteristics. In this work, the functional relationship between the coal blend properties (ash, volatile matter, average vitrinite reflectance, crucible swelling number, total reactives, vitrinite distribution V9–V13 and basicity index) and the corresponding coke CSR has been mapped using an adaptive neurofuzzy inference system (ANFIS). The ANFIS model is formulated with different sets of coal blend properties as input variable, and the singular value decomposition and QR factorisation based techniques have been employed for model reduction. It has been found that the developed ANFIS model predicts the CSR with reasonable accuracy.

Cooling and stabilization by collisions in a mixed ion–atom system

In mixed systems of trapped ions and cold atoms, the ions and atoms can coexist at different temperatures. This is primarily due to their different trapping and cooling mechanisms. The key questions of how ions can cool collisionally with cold atoms and whether the combined system allows stable coexistence, need to be answered. Here we experimentally demonstrate that rubidium ions cool in contact with magneto-optically trapped rubidium atoms, contrary to the general experimental expectation of ion heating. The cooling process is explained theoretically and substantiated with numerical simulations, which include resonant charge exchange collisions. The mechanism of single collision swap cooling of ions with atoms is discussed. Finally, it is experimentally and numerically demonstrated that the combined ion-atom system is intrinsically stable, which is critical for future cold chemistry experiments with such systems.

Light-Assisted Ion-Neutral Reactive Processes in the Cold Regime: Radiative Molecule Formation versus Charge Exchange

We present a combined experimental and theoretical study of cold reactive collisions between laser-cooled Ca+ ions and Rb atoms in an ion-atom hybrid trap. We observe rich chemical dynamics which are interpreted in terms of nonadiabatic and radiative charge exchange as well as radiative molecule formation using high-level electronic structure calculations. We study the role of light-assisted processes and show that the efficiency of the dominant chemical pathways is considerably enhanced in excited reaction channels. Our results illustrate the importance of radiative and nonradiative processes for the cold chemistry occurring in ion-atom hybrid traps.

Cold collisions of highly rotationally excited CO2with He: The prospects for cold chemistry with super-rotors

Building on recent advances in ultrafast lasers and methods to slow molecules, an experiment is proposed to produce translationally cold CO${}_{2}$ super-rotors ($j\ensuremath{\sim}200$) by combining an optical centrifuge with helium-buffer-gas cooling. Quantum mechanical calculations of the complex scattering length for He-CO${}_{2}$ collisions demonstrate that the efficiency of rotational quenching decreases rapidly with increasing rotational excitation $j$ in the ultracold regime. Extrapolating to helium cryogenic temperatures, rotational quenching is predicted to remain inefficient up to $\ensuremath{\sim}$1 K, allowing for the possible creation of a beam of translationally cold, rotationally hot molecules.

Cold Chemistry with Ionic Partners: Quantum Features of HeH+(1Σ) with H(1S) at Ultralow Energies

Quantum reactive calculations are presented for an ion-atom reaction involving the HeH(+)cation and its destruction via a barrierless interaction with H atoms. The range of collision energies considered is that of a cold trap regime (around and below millikelvin) where the ionic partner could be spatially confined. Specific resonant features caused by the interplay of the strong ionic interaction with the very slow partners' dynamics are found and analyzed. Indications are also given on the consequences of the abstraction mechanism that acts for this reaction at low energies.

Cold chemistry with electronically excited Ca+ Coulomb crystals

Rate constants for chemical reactions of laser-cooled Ca(+) ions and neutral polar molecules (CH(3)F, CH(2)F(2), or CH(3)Cl) have been measured at low collision energies (<E(coll)>/k(B)=5-243 K). Low kinetic energy ensembles of (40)Ca(+) ions are prepared through Doppler laser cooling to form "Coulomb crystals" in which the ions form a latticelike arrangement in the trapping potential. The trapped ions react with translationally cold beams of polar molecules produced by a quadrupole guide velocity selector or with room-temperature gas admitted into the vacuum chamber. Imaging of the Ca(+) ion fluorescence allows the progress of the reaction to be monitored. Product ions are sympathetically cooled into the crystal structure and are unambiguously identified through resonance-excitation mass spectrometry using just two trapped ions. Variations of the laser-cooling parameters are shown to result in different steady-state populations of the electronic states of (40)Ca(+) involved in the laser-cooling cycle, and these are modeled by solving the optical Bloch equations for the eight-level system. Systematic variation of the steady-state populations over a series of reaction experiments allows the extraction of bimolecular rate constants for reactions of the ground state ((2)S(1/2)) and the combined excited states ((2)D(3/2) and (2)P(1/2)) of (40)Ca(+). These results are analyzed in the context of capture theories and ab initio electronic structure calculations of the reaction profiles. In each case, suppression of the ground state rate constant is explained by the presence of a submerged or real barrier on the ground state potential surface. Rate constants for the excited states are generally found to be in line with capture theories.

Water binding sites in 2-para- and 2-ortho-fluorophenylethanol: A high-resolution UV experiment and ab initio calculations

The singly hydrated complexes of the flexible prototype molecules 2-para-fluorophenylethanol and 2-ortho-fluorophenylethanol have been investigated by combination of high-resolution resonance-enhanced two-photon ionization spectroscopy in a cold supersonic beam and quantum chemistry ab initio calculations. We have identified the conformational structures of the above complexes, which correspond to water binding to the most stable gauche monomer's conformers in both cases. No structural changes of the host molecules upon the attachment of a single water molecule have been found. For the 2-ortho-fluorophenylethanol-water complex we have observed an additional structure with one of the higher-in-energy gauche conformers of the monomer. This corroborates the assumption that the complexation with water stabilizes the higher-energy conformer of the monomer, precluding it from relaxation to the lowest-energy geometry.

Deuterium chemistry in the Orion Bar PDR

High levels of deuterium fractionation in gas-phase molecules are usually associated with cold regions, such as prestellar cores. Significant fractionation ratios are also observed in hot environments such as hot cores or hot corinos, where they are believed to be produced by the evaporation of the icy mantles surrounding dust grains, and thus are remnants of a previous cold (either gas-phase or grain surface) chemistry. The recent detection of DCN towards the Orion Bar, in a clump at a characteristic temperature of 70K, has shown that high deuterium fractionation can also be detected in PDRs. The Orion Bar clumps thus appear as a good environment for the observational study of deuterium fractionation in luke-warm gas, allowing to validate chemistry models in a different temperature range, where dominating fractionation processes are predicted to be different than in cold gas (< 20K). We aimed at studying observationally in detail the chemistry at work in the Orion Bar PDR, to understand if DCN is produced by ice mantle evaporation, or is the result of warm gas-phase chemistry, involving the CH2D+ precursor ion (which survives higher temperatures than the usual H2D+ precursor). Using the APEX and the IRAM 30m telescopes, we targetted selected deuterated species towards two clumps in the Orion Bar. We confirmed the detection of DCN and detected two new deuterated molecules (DCO+ and HDCO) towards one clump in the Orion Bar PDR. Significant deuterium fractionations are found for HCN and H2CO, but a low fractionation in HCO+. We also give upper limits for other molecules relevant for the deuterium chemistry. (...) We show evidence that warm deuterium chemistry driven by CH2D+ is at work in the clumps.

Geochemistry of the thermal springs of Mount Taftan, southeastern Iran

Thermal and cold water chemistry from the southern flank of Mount Taftan was investigated in order to discriminate among hydrochemical facies, isotopic characteristics, geothermal reservoir and identify the major geochemical processes that affect water composition. The waters from both the hot and cold springs show high total dissolved solids content, and are strongly to lightly acidic. Calcium is the dominant cation; in terms of anions, the Taftan hot springs are Cl–SO 4 type. There is also a HCO 3 type cold spring. The SO 4/Cl ratios on an SO 4–Cl–HCO 3 diagram confirm the volcanic origin of the hot waters. Conservative elements indicate that the three types of analysed water have similar origin and the difference in concentration is due to dilution of thermal water with almost shallow fresh groundwater, not affecting the elements' proportions. Also, the retrogressive δ 18O-enrichment with respect to the meteoric water line (MWL), confirms that thermal waters (andesitic water) have been diluted by shallow waters of meteoric origin. Comparison of the chemistry of thermal and cold springs and other evidences are indicative of an immature hydrothermal water system in Taftan volcano. Because of waters immaturity, temperatures in the geothermal reservoir in Taftan region cannot be estimated accurately by applying Na–K, K–Mg and quartz geothermometers.

Stopping supersonic oxygen with a series of pulsed electromagnetic coils: A molecular coilgun

We report the stopping of a molecular oxygen beam, using a series of pulsed electromagnetic coils. A series of coils is fired in a timed sequence to bring the molecules to near rest, where they are detected with a quadrupole mass spectrometer. Applications to cold chemistry are discussed.

Cold controlled chemistry

Collisions of molecules in a thermal gas are difficult to control. Thermal motion randomizes molecular encounters and diminishes the effects of external radiation or static electromagnetic fields on intermolecular interactions. The effects of the thermal motion can be reduced by cooling molecular gases to low temperatures. At temperatures near or below 1 K, the collision energy of molecules becomes less significant than perturbations due to external fields. At the same time, inelastic scattering and chemical reactions may be very efficient in low-temperature molecular gases. The purpose of this article is to demonstrate that collisions of molecules at temperatures below 1 K can be manipulated by external electromagnetic fields and to discuss possible applications of cold controlled chemistry. The discussion focuses on molecular interactions at cold (0.001-2 K) and ultracold (<0.001 K) temperatures and is based on both recent theoretical and experimental work. The article concludes with a summary of current challenges for theory and experiment in the research of cold molecules and cold chemistry.

Slow beams of massive molecules

Slow beams of neutral molecules are of great interest for a wide range of applications, from cold chemistry through precision measurements to tests of the foundations of quantum mechanics. We report on the quantitative observation of thermal beams of perfluorinated macromolecules with masses up to 6000?amu, reaching velocities down to 11?m/s. Such slow, heavy and neutral molecular beams are of importance for a new class of experiments in matter-wave interferometry and we also discuss the requirements for further manipulation and cooling schemes with molecules in this unprecedented mass range.

Cold atoms and molecules from fragmentation of deceleratedSO2

Using the example of the $\mathrm{S}{\mathrm{O}}_{2}$ molecule, we will discuss photodissociation at threshold as a possibility for producing cold molecules or atoms. The fragments SO and O have low excess energy and are free radicals with high interest for applications like cold chemistry. The threshold behavior is tunable by external fields and shows great similarity to Feshbach resonance studies in cold atom collisions. To take full advantage of the cold fragmentation, it is necessary to dissociate within a cold sample of molecules. In our initial experiments we have demonstrated substantial Stark deceleration of $\mathrm{S}{\mathrm{O}}_{2}$.

Molecules in the cold environment of a supersonic free-jet beam: from spectroscopy of neutral–neutral interactions to a test of Bell's inequality

The supersonic free-jet expansion technique has been used in different fields of research in physics, physical chemistry and chemistry to study vibrational and rotational molecular structures in ground and excited electronic energy states as well as in cold chemistry to study chemical reactions in a unique environment. The supersonic beam technique, as a widely used method in laser spectroscopy of molecules, exploits a source of monokinetic, rotationally and vibrationally cold molecules, that are very weakly bound in their ground electronic states (van der Waals molecules). In experiments at Jagiellonian University the supersonic free-jet beam serves as a source of ground-state van der Waals objects in studies of neutral–neutral interactions between group 12 metal (M = Zn, Cd, Hg) and noble gas (NG) atoms. Recently, the method has been applied as a source of entangled 199Hg atom pairs in order to test Bell's inequality in an experiment at Texas A&M University.

Determination of metabolic stability of positron emission tomography tracers by LC–MS/MS: An example in WAY-100635 and two analogues

A method is presented for determination of microsomal metabolic stability of potential positron emission tomography (PET) tracers by LC–MS/MS in the lower nm range. The PET tracers used for the study were the serotonin receptor antagonist WAY-100635 and two potential tracer analogues. The sensitivity permitted the substrates to be directly collected from PET radiolabelling batches, containing very low amounts of substance (0.3–7 μg), for subsequent metabolic stability incubations. Sample preparation was minimal, with addition of internal standard, acetonitrile and a fast centrifugation step, as a result of the low protein concentration of the microsome solutions. Linearity ( R 2 ≥ 0.99), precision (inter-assay R.S.D. < 7%) and accuracy (bias ≤8%) for the tested concentration range 0.5–5 nM proved to be well within accepted limits. No significant differences in metabolic rates were detected using substrates from cold (non-labelling) chemistry syntheses and PET labelling batches, indicating the validity of using substrates from the latter source. A para-methoxy-benzamide analogue (MeO-WAY) displayed a significantly lower rate of metabolism compared to WAY-100635, whereas a para-iodo-benzamide analogue was more susceptible to metabolic transformation. LC–MS/MS Analysis of formed metabolites from WAY-100635 and MeO-WAY suggested similar metabolic pathways, with hydroxylation, demethylation and dearylation reactions. The main metabolic route in humans, amide hydrolysis, was not observed with the rat liver microsome assay.

Continuous Loading of an Electrostatic Trap for Polar Molecules

A continuously operated electrostatic trap for polar molecules is demonstrated. The trap has a volume of approximately 0.6 cm3 and holds molecules with a positive Stark shift. With deuterated ammonia from a quadrupole velocity filter, a trap density of approximately 10(8) cm(-3) is achieved with an average lifetime of 130 ms and a motional temperature of approximately 300 mK. The trap offers good starting conditions for high-precision measurements, and can be used as a first stage in cooling schemes for molecules and as a "reaction vessel" in cold chemistry.

Molecular processes in the early Universe

Molecular processes first took place in the Universe in the recombination era as the expanding Universe cooled adiabatically and recombined when the cooling radiation field ran out of photons energetic enough to cause photoionization. The formation of neutral helium heralded the dawn of chemistry as the neutral atoms participated in processes of radiative association to form molecular ions. Dissociative recombination of the molecular ions produced neutral atoms and accelerated the conversion of the ionized plasma into a neutral gas. The subsequent chemistry involved hydrogen, deuterium, helium and lithium created earlier in a brief period of nucleosynthesis. With the continued expansion the Universe became cold and dark and chemistry came to a temporary end until the formation and gravitational collapse of the first distinct cosmological objects. Heavy elements were made, a new source of radiation – starlight – appeared and a richer chemistry was initiated.

Mixing efficiency measurements using a modified cold chemistry technique

The efficient mixing of fluids in compressible shear layers is still of fundamental importance to high-speed propulsion. To further understand the role of compressibility, measurements of mixing efficiency are performed in a convective Mach number=2.64 shear layer. The mean scalar field and estimated mixing efficiency are measured using a new “cold chemistry” technique utilizing the quenching of nitric oxide laser-induced fluorescence to mark regions of molecularly mixed fluid. Several different quenching partners are used to achieve statistically converged results using fewer images than previous techniques. The mixing efficiency (δm/δ) measured in this study at a Reynolds number of 1.9×106 is 0.64, following an increasing trend with both Reynolds number and compressibility when taken with previously measured cold chemistry results.

Mixing enhancement in compressible shear layers via sub-boundary layer disturbances

Mixing enhancement results are presented for compressible (convective Mach number 0.63) planar shear layers perturbed by 2D and 3D disturbances located within the supersonic-side splitter tip boundary layer. The disturbances were parametrically varied in shape, spacing, and thickness, and for each geometry time-resolved end-, side-, and plan-view visualizations of mixed fluid were obtained. The mixing layer thickness and growth rate are measured directly from the averaged images. As an indicator of the pressure loss induced by each disturbance geometry, the streamwise static pressure distribution is also recorded. The visualizations reveal that discrete 3D disturbances induce appreciable spanwise convolution, streamwise structure, and thickening of the mixing layer with disturbances as thin as 5% of the boundary layer displacement thickness. The optimal disturbance appears to have an angle of 30° to the streamwise direction and be located at the splitter tip, rather than upstream. Panoramic side-views show that the far-field growth rate increases (45% in one case) for certain discrete 3D disturbances but not 2D disturbances, despite equivalent area blockage. For the most promising geometry, quantitative measurements of the mixing layer thickness, probability of mixed fluid, and mixing efficiency were made using cold chemistry planar laser-induced fluorescence. The perturbed layer shows a slight improvement (7%) in mixing efficiency and a large increase (48%) in layer thickness, indicating that gains in the total amount of mixed fluid occur primarily by layer thickening.