56 research outputs found
Hyperon polarization and single spin left-right asymmetry in inclusive production processes at high energies
It is shown that the polarization of hyperons observed in high energy
collisions using unpolarized hadron beams and unpolarized nucleon or nuclear
targets is closely related to the left-right asymmetries observed in single
spin inclusive hadron production processes. The relationship is most obvious
for the production of the hyperons which have only one common valence quark
with the projectile. Examples of this kind are given. Further implications of
the existence of large polarization for hyperon which has two valence quarks in
common with the projectile and their consequences are discussed. A comparison
with the available data is made. Further tests are suggested.Comment: REVTeX, 12 pages, 2 figures embedde
Reactions of the CN Radical with Benzene and Toluene: Product Detection and Low-Temperature Kinetics
Cyclic Versus Linear Isomers Produced by Reaction of the Methylidyne Radical (CH) with Small Unsaturated Hydrocarbons
Crossed Molecular Beams Study on the Formation of Vinylacetylene in Titan’s Atmosphere
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Reactions of the CN Radical with Benzene and Toluene: Product Detection and Low-Temperature Kinetics
Low-temperature rate coefficients are measured for the CN + benzene and CN + toluene reactions using the pulsed Laval nozzle expansion technique coupled with laser-induced fluorescence detection. The CN + benzene reaction rate coefficient at 105, 165, and 295 K is found to be relatively constant over this temperature range, (3.9−4.9) × 10−10 cm3 molecule−1 s−1. These rapid kinetics, along with the observed negligible temperature dependence, are consistent with a barrierless reaction entrance channel and reaction efficiencies approaching unity. The CN + toluene reaction is measured to have a rate coefficient of 1.3 × 10−10 cm3 molecule−1 s−1 at 105 K. At room temperature, nonexponential decay profiles are observed for this reaction that may suggest significant back-dissociation of intermediate complexes. In separate experiments, the products of these reactions are probed at room temperature using synchrotron VUV photoionization mass spectrometry. For CN + benzene, cyanobenzene (C6H5CN) is the only product recorded with no detectable evidence for a C6H5 + HCN product channel. In the case of CN + toluene, cyanotoluene (NCC6H4CH3) constitutes the only detected product. It is not possible to differentiate among the ortho, meta, and para isomers of cyanotoluene because of their similar ionization energies and the 40 meV photon energy resolution of the experiment. There is no significant detection of benzyl radicals (C6H5CH2) that would suggest a H-abstraction or a HCN elimination channel is prominent at these conditions. As both reactions are measured to be rapid at 105 K, appearing to have barrierless entrance channels, it follows that they will proceed efficiently at the temperatures of Saturn’s moon Titan (100 K) and are also likely to proceed at the temperature of interstellar clouds (10−20 K)
Reactions of small carbon-bearing radicals with unsaturated hydrocarbons: Product detection and low temperature kinetics
We report on results from two experimental techniques concerned with the reactions of small carbon based radicals (CN and CH) with unsaturated hydrocarbons. First, low temperature (100-300K) kinetic studies using a pulse Laval nozzle technique probe the reactions of the CN radical with benzene and toluene. The CN + benzene is found to be a fast, barrierless reaction. But in the case of toluene, two reaction pathways are in competition, one of which back dissociates to the reactants. The implications for the atmosphere of Titan are discussed. Product detection studies undertaken at the Advanced Light Source (ALS) using synchrotron coupled multiplexed mass spectrometry comprise the other component of this undertaking. The CH + C2H2 reaction is investigated by detecting the products and furthermore the reaction pathways are probed using isomer resolved mass spectrometry and isotopic labelling
Gas Phase Reactive Collisions at very Low Temperature: Recent Experimental Advances and Perspectives
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