Differentielle Streuquerschnitte bei der Wechselwirkung neutraler Molek�le Messungen der Kleinwinkelstreuung

Helbing, R.; Pauly, H.

doi:10.1007/bf01379211

Cited by 62 publications

(13 citation statements)

References 0 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…In contrast, the quantum theory for such an attractive potential gives instead a large but finite cross section. Figure 4 illustrates the contrast between classical and quantum cross sections for elastic scattering at small angles, for a system subject to an attractive r −6 potential [48]. In effect, the uncertainty principle imposes a "cut-off angle," denoted here by θ 0 .…”

Section: Collision Cross Sectionsmentioning

confidence: 99%

Molecular beams entwined with quantum theory: A bouquet for Max Planck

Herschbach

2001

Ann. Phys.

View full text Add to dashboard Cite

In an era when the fledgling quantum theory was "uncertain and even gave contradictory answers," Otto Stern undertook to employ molecular beams to test directly fundamental aspects of the theory. During 1921During -1935, this led to five decisive experiments reviewed here, resulting in the discovery or demonstration of space quantization, de Broglie matter waves, anomalous magnetic moments of the proton and neutron, recoil of an atom on emission of a photon, and the limitation of scattering cross-sections for molecular collisions imposed by the uncertainty principle.

show abstract

Section: Collision Cross Sectionsmentioning

confidence: 99%

Molecular beams entwined with quantum theory: A bouquet for Max Planck

Herschbach

2001

Ann. Phys.

View full text Add to dashboard Cite

show abstract

“…The glancing collisions with background atoms make our study more difficult, but are of some interest in their own right [11]. The collisional energies are very high and hundreds of partial waves are involved, yet a classical treatment of the collisions yields incorrect results.…”

Section: Measurement Of Cs-cs Elastic Scattering At T = 30 //Kmentioning

confidence: 99%

Measurement of Cs-Cs elastic scattering atT=30 μK

et al. 1993

View full text Add to dashboard Cite

We have measured the elastic collision cross section for spin polarized atomic cesium. Neutral cesium atoms are optically cooled, then loaded into a dc magnetic trap. We infer the scattering rate from the rate at which anisotropics in the initial energy distribution are observed to relax. The cross section for F = 3, mf = -3 on ^^3, w/r = -3 is 1.5(4) x 10~1 2 cm 2 , and is independent of temperature from 30 to 250 ^K. This determination clarifies the technical requirements for attaining Bose-Einstein condensation in a magnetically trapped Cs vapor. We also study heating due to glancing collisions with 300 K background Cs atoms.PACS numbers: 34.40.+ n, 05.30Jp, 32.80.Pj, 34.50.-s Recent advances in optical trapping and cooling techniques have allowed collision studies in an entirely new regime of temperatures. In this regime of mK or even colder temperatures, collisions take on unusual characteristics, and often have cross sections many orders of magnitude different from that observed at previously attainable temperatures. Studies of ultralow-temperature collisions have investigated several inelastic processes which cause loss from optical traps: two-photon quasimolecular photoionization [1], photon-assisted collisions [2,3], and hyperfine-state changing collisions [2,4]. All of these processes are inelastic, and while they involve low initial energies for the atoms involved, the final states have kinetic energies of 1 K or greater. It appears that this allows these processes to be treated semiclassically, although the exact accuracy of such treatments is currently a topic of debate. In the work presented here, we examine elastic collisions in which the initial and final energies are both much less than 1 mK. In order to study such low-energy collisions we have developed techniques for observing collisions in very cold samples of magnetically trapped atoms. From these measurements, we deduce the s-wave collision cross section.The elastic scattering cross section is of particular interest because of its importance in determining the experimental feasibility of achieving Bose-Einstein condensation (BEC) in a cesium vapor. As demonstrated in experiments with spin polarized hydrogen [5], evaporative cooling of magnetically trapped atoms is a promising strategy for achieving the temperature and density necessary for the BEC phase transition, because evaporative cooling does not have the density and temperature limitations encountered in optical cooling and trapping [2,6].To study the very low energy elastic collisions, we first accumulate Cs atoms in a Zeeman-shift optical trap (ZOT) in a low pressure cell [7]. The atoms are then optically cooled and spin polarized in the F = 3, m/r = -3 state in preparation for magnetic trapping. After all laser light is shut off, magnetic fields are turned on around the atoms in situ [7], thereby trapping them.In this work we use a type of dc magnetic trap which has been previously proposed but, to our knowledge, never used to trap neutral atoms. The field coils consist of wire woun...

show abstract

“…No structure is apparent. The small angle slope of the cross-section deviates from the values : -7/3, expected for a letter to the Editor L21 pair of fast-rotating dipoles or -8/3, for slowly-rotating dipoles (Helbing and Pauly 1964) (Cross et al 1966). Small angle inelastic collisions (Donohue et al 1972) could be the source of the anomalous slope, and are at present under investigation.…”

mentioning

confidence: 62%

Spatial topographical systems of Poincaré and comparison systems

Шамолин¹

1997

Russ. Math. Surv.

View full text Add to dashboard Cite

The differential collision cross section for the scattering of water molecules has been measured up to 25 degrees at 20 x erg relative energy. The small angle behaviour of the cross section cannot be described in terms of elastic scattering between fast (nor slow) rotating dipoles. The Lennard-Jones (12-6) potential that best describes the wide angle portion of the cross section has a well depth of 5.8 x erg.

show abstract

Differentielle Streuquerschnitte bei der Wechselwirkung neutraler Molek�le Messungen der Kleinwinkelstreuung

Cited by 62 publications

References 0 publications

Molecular beams entwined with quantum theory: A bouquet for Max Planck

Molecular beams entwined with quantum theory: A bouquet for Max Planck

Measurement of Cs-Cs elastic scattering atT=30 μK

Spatial topographical systems of Poincaré and comparison systems

Contact Info

Product

Resources

About