Physics:Molecular beam
A molecular beam is produced by allowing a gas at higher pressure to expand through a small orifice into a chamber at lower pressure to form a beam of particles (atoms, free radicals, molecules or ions) moving at approximately equal velocities, with very few collisions between the particles. Molecular beams are useful for fabricating thin films in molecular beam epitaxy and artificial structures such as quantum wells, quantum wires, and quantum dots. Molecular beams have also been applied as crossed molecular beams. The molecules in the molecular beam can be manipulated by electrical fields and magnetic fields.[1] Molecules can be decelerated in a Stark decelerator or in a Zeeman slower.
History
The first to study atomic beam experiments was Louis Dunoyer de Segonzac 1911, but were simple experiments to confirm that atoms travelled in straight lines when not acted on by external forces.[2] Since 1921, the teams of Otto Stern in University of Hamburg and University of Frankfurt am Main, improved and pioneered the experiments with atomic beams, and later with molecular beams. The advances of Stern and collaborators led to decisive discoveries including: the discovery of space quantization; de Broglie matter waves; anomalous magnetic moments of the proton and neutron; recoil of an atom of emission of a photon; and the limitation of scattering cross-sections for molecular collisions imposed by the uncertainty principle[2]
However, the first paper on molecular beams was by Hartmut Kallmann and Fritz Reiche, who before Stern who started with atoms, were interested in dipole moments and the deflection of beams of polar molecules (not just atoms) in an inhomogeneous electric field.[3] In 1922, with Walther Gerlach, Stern rushed to publish their results on the Stern–Gerlach experiment demonstrating the existence of the spin, after reading on the experiments of Kallman and Reiche.[2] However the paper of Kallman and Reiche would go largely unnoticed until its rediscovery 2009.[4]
The first to report on the relationship between dipole moments and deflection in a molecular beam (using binary salts such as KCl) was Erwin Wrede in 1927.[5][4] In 1939 Isidor Rabi invented a molecular beam magnetic resonance method in which two magnets placed one after the other create an inhomogeneous magnetic field. The method was used to measure the magnetic moment of several lithium isotopes with molecular beams of LiCl, LiF and dilithium.[6][7] This method is a predecessor of NMR. The invention of the maser in 1957 by James P. Gordon, Herbert J. Zeiger and Charles H. Townes was made possible by a molecular beam of ammonia and a special electrostatic quadrupole focuser.[8]
The study of molecular beam led to the development of molecular-beam epitaxy in the 1960s.
See also
- Norman Ramsey
- John B. Fenn
- F.M. Devienne
- Dudley R. Herschbach
References
- ↑ van de Meerakker, Sebastiaan Y. T.; Bethlem, Hendrick L.; Vanhaecke, Nicolas; Meijer, Gerard (2012-03-27). "Manipulation and Control of Molecular Beams". Chemical Reviews (American Chemical Society (ACS)) 112 (9): 4828–4878. doi:10.1021/cr200349r. ISSN 0009-2665. PMID 22449067.
- ↑ 2.0 2.1 2.2 Ramsey, N. F. (1988). "Molecular beams: our legacy from Otto Stern" (in en). Zeitschrift für Physik D Atoms, Molecules and Clusters 10 (2-3): 121–125. doi:10.1007/BF01384845. ISSN 0178-7683. http://link.springer.com/10.1007/BF01384845.
- ↑ "Kallmann, H.; Reiche, F. (1921). "Über den Durchgang bewegter Moleküle durch inhomogene Kraftfelder" (in de). Zeitschrift für Physik (Springer Science and Business Media LLC) 6 (1): 352–375. doi:10.1007/bf01327996. ISSN 1434-6001. https://zenodo.org/record/2475237.
- ↑ 4.0 4.1 Friedrich, Bretislav; Schmidt-Böcking, Horst (2021), Friedrich, Bretislav; Schmidt-Böcking, Horst, eds., "Otto Stern’s Molecular Beam Method and Its Impact on Quantum Physics" (in en), Molecular Beams in Physics and Chemistry (Cham: Springer International Publishing): pp. 37–88, doi:10.1007/978-3-030-63963-1_5, ISBN 978-3-030-63962-4, https://link.springer.com/10.1007/978-3-030-63963-1_5, retrieved 2023-08-03
- ↑ "Wrede, Erwin (1927). "Über die Ablenkung von Molekularstrahlen elektrischer Dipolmoleküle im inhomogenen elektrischen Feld" (in de). Zeitschrift für Physik (Springer Science and Business Media LLC) 44 (4–5): 261–268. doi:10.1007/bf01391193. ISSN 1434-6001.
- ↑ Rabi, I. I.; Millman, S.; Kusch, P.; Zacharias, J. R. (1939-03-15). "The Molecular Beam Resonance Method for Measuring Nuclear Magnetic Moments. The Magnetic Moments of 3Li6, 3Li7 and 9F19". Physical Review (American Physical Society (APS)) 55 (6): 526–535. doi:10.1103/physrev.55.526. ISSN 0031-899X.
- ↑ The Rabi molecular-beam method - The Feynman Lectures on Physics
- ↑ Gordon, J. P.; Zeiger, H. J.; Townes, C. H. (1954-07-01). "Molecular Microwave Oscillator and New Hyperfine Structure in the Microwave Spectrum of NH3". Physical Review (American Physical Society (APS)) 95 (1): 282–284. doi:10.1103/physrev.95.282. ISSN 0031-899X.
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