A Source of a Seeded Supersonic Beam of Alkali Halide Molecules
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A Source of a Seeded Supersonic Beam of Alkali Halide Molecules V. M. Azriel’a, V. M. Akimova,*, E. V. Ermolovaa, D. B. Kabanova, L. I. Kolesnikovaa, L. Yu. Rusina, and M. B. Sevryuka a Talrose
Institute for Energy Problems of Chemical Physics, Semenov Federal Research Center of Chemical Physics, Russian Academy of Sciences, Moscow, 119334 Russia *e-mail: [email protected] Received May 15, 2020; revised June 5, 2020; accepted June 10, 2020
Abstract—The design of a source of a seeded supersonic beam of alkali halide molecules or other vaporized solids is described. At a carrier gas (hydrogen or helium) stagnation pressure of 0.5–5 atm, a stagnation temperature of 1000 K, and a partial seed species pressure of 10–2 Torr, the intensity of the salt beam was 1014 sr–1 s–1 and the energy of molecules in the beam varied from 5.5 to 7.5 eV for a mixture with helium and from 7.5 to 15.5 eV for a mixture with hydrogen. The modular design of the source provides the easy replacement of its functional units. DOI: 10.1134/S0020441220060020
INTRODUCTION The practice of using molecular beams in scientific research and engineering shows that the success of a work strongly depends on the quality of the methods used to generate beams and detect the results of their interaction. Seeded supersonic molecular beams of neutral particles, i.e., atoms, molecules, clusters, are widely used for studying elastic, inelastic, and reactive scattering of atoms and molecules, relaxation processes in jets, determining the potential energy surface, studying the scattering of atoms and molecules on solid surfaces, and in many other experiments, as well as technological processes. These beams are widely used due to the significant range of realized energies (from units to tens of electron volts) for heavy atoms and molecules, as well as due to a narrow velocity distribution of beam particles. Such characteristics are achieved during gas-dynamic acceleration when a small impurity of a heavy component of the mixture in a light carrier gas (usually molecular hydrogen or helium) flows from a high-pressure zone through a nozzle (with a diameter that exceeds the free path in the high-pressure zone) into a vacuum [1]. In the limiting case, the speed of the heavy component of the mixture increases to the carrier gas speed with a corresponding increase in energy by Mh/Ml times according to the formula
E = [γkT /(γ – 1)]M h /M l , where E is the energy of a molecule of the heavy component; γ = cp/cv is the ratio of the specific heats of the carrier gas (γ = 7/5 for hydrogen and γ = 5/3 for
helium); k = 1.04 × 10–19 Torr cm3 K–1 is the Boltzmann constant; T is the nozzle temperature; and Mh and Ml are the masses of molecules of the heavy and light beam components, respectively. The beam energy can be changed by varying the stagnation pressure, temperature, and mixture composition. The beam is then formed by a skimmer and a collimator, which are located in differentially evacuated vacuum chambers. Seeded sources of beams of condensing substan
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