Crossed beam studies

Laser photolysis of a precursor may also be used to generate a reagent. In a crossed-beam study of the D + FI2 reaction [24], a hypertliennal beam of deuterium atoms (0.5 to 1 eV translational energy) was prepared by 248 mn photolysis of DI. This preparation method has been widely used for the preparation of molecular free radicals, both in beams and in experiments in a cell, with laser detection of the products. Laser photolysis as a method to prepare reagents in experiments in which the products are optically detected is fiirtlier discussed below. 

The setup used for crossed beam experiments is basically the same apparatus used in the H2O photodissociation studies but slightly modified. In the crossed beam study of the 0(1D) + H2 — OH + H reaction and the H + HD(D2) — H2(HD) + D reaction, two parallel molecular beams (H2 and O2) were generated with similar pulsed valves. The 0(1D) atom beam was produced by the 157 photodissociation of the O2 molecule through the Schumann-Runge band. The 0(1D) beam was then crossed at 90° with the... 

Recent studies with a crossed-beam apparatus not only show that the products shown above are the correct ones, but that both the linear and cyclic isomers, each of which is a detected interstellar molecule, are formed.47 Crossed-beam studies also show that other reactions between C atoms and unsaturated hydrocarbons proceed to form similar products 48... 

Crossed beam studies involving both neutrals and ions will provided detailed information relating to the potential energy surfaces and reaction mechanisms for organometallic reactions (19). These studies are especially revealing when the reactions are direct and involve intermediates whose lifetime does not exceed a rotational period. 

Shah, M.B., Elliot, D.S. and Gilbody, H.B. (1987). Pulsed crossed-beam study of the ionisation of atomic hydrogen by electron impact. J. Phys. B At. Mol. Phys. 20 3501-3514. 

K. Liu, Crossed-beam studies of neutral reactions State-specific differential cross sections, Annu. Rev. Phys. Chem. 52 (2001) 139. 

K. Liu, Recent advances in crossed-beam studies of bimolecular reactions, J. Chem. Phys. 125,132307 (2006). 

This chapter concentrates on the experimental determination of product energy distributions and their interpretation in terms of the dynamics of collisions. In a volume concerned with excited states, it seemed appropriate to bias the article in favor of the spectroscopic methods and results, at the expense of the crossed-beam studies. Electronically adiabatic reactions, which pass smoothly from reactants to products in their electronic ground states, are emphasized, since the results of such processes may be compared with trajectories computed with the equations of classical, rather than wave, mechanics, and the effects of kinematic factors on the sharing of energy can be explored. 

Propyl cationic intermediates have also been proposed by Smith et al. (1975) in crossed beam studies of methyl cation with ethylene to explain the scrambling of isotopes that results from reaction with labelled substrates (e.g. or C2D4). Linear ions (e.g. n-propyl and isopropyl cations) are favoured over protonated cyclopropanes for these high energy species which dissociate into CH4 + C,H+... 

Threshold energy for formation of HD + CDjBr Crossed-beam study of K + HF as a function of rotational state and translational energy Photoreactions leading to the production of laser snow studied in crossed-beam apparatus Study of CsH formation... 

Supersonic beam of Li used to measure molecular constants of LiJ Crossed-beam study of NaJ formation in the presence of intense, non-resonant radiation... 

Liu, K. Excitation functions of elementary chemical reactions a direct link from crossed-beam dynamics to thermal kinetics Int. Rev. Phys. Chem. 2001, 20, 189-217. Liu K. Crossed-beam studies of neutral reactions state-specific differential cross sections. Annu. Rev. Phys. Chem. 2001, 52, 139-159. 

Alagia, M. Balucani, N. Cartechini, L. Casavecchia, P. Volpi, G.G. Dynamics of chemical reactions of astrophysical interest. In Molecules in Astrophysics Probes and Processes, I AU Symposium 178. van Dishoek, E.F., Ed., Kluwer Academic Publishers, Dordrecht, 1996, 271-280. Alagia, M. Balucani, N. Casavecchia, P. Stranges, D. Volpi, G.G. Crossed beam studies of four-atom reactions the dynamics of OH -I- CO. J. Chem. Phys. 1993, 98, 8341-8344. Alagia, M. Balucani, N. Casavecchia, P. Stranges, D. Volpi, G.G. Crossed beam studies of four-atom reactions the dynamics of OH + D2. J. Chem. Phys. 1993, 98, 2459-2462. 

Bergeat, A. Volpi, G.G. Crossed beam studies of elementary reactions of N and C atoms and CN radicals of importance in combustion. Faraday Discuss. 

The molecular beam technique, which was first applied to a chemical system in 1954 by Bull and Moon [165] and the first crossed beam study of Datz and Schmidt [123] in 1967, has reached maturity with the development by Greene and co-workers [373] in 1974 of a molecular beam apparatus for student teaching experiments. Future developments will probably be in the study of the reactions of beams of metals other than alkali and alkaline earths and atoms and radicals. Hopefully, the theories of such reactions will merge with the theories of ion—molecule reactions. 

Crossed Beam Studies of Chemical Kinetics Using Radiotracer Techniques... 

Shortly after these results were published, Bernstein and coworkers (10,11) completed a crossed beam study of the reaction of K atoms with HBr and DBr, with velocity selection of the incident K-atom beam and velocity analysis of the KBr product. Analysis of the data showed that the product KBr c.m. angular distributions are broadly backward-peaked for K + HBr and nearly isotropic for K + DBr and that the recoil velocity distributions are broad and extend to the maximum value allowed energetically. These results differ considerably from the results for K + TBr since (i) when taken together, the angular distributions imply that the KBr product shifts nonmonotonically from broadly backward-peaked to nearly isotropic to sharply backward-peaked with the isotopic substitutions HBr DBr TBr and (ii) the mean recoil energy is much lower (and therefore the product excitation much higher) for K + TBr. These differences are still unresolved at this writing. 

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