Observation of High-Resolution Differential Cross Section of Polarized, Rotationally State-Selected LiF on Ar

Tsou, Len‐Yuan; Auerbach, Daniel J.; Wharton, Lennard

doi:10.1103/physrevlett.38.20

Cited by 31 publications

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“…Firstly, experimental data on differential scattering of m-selected molecules were not available, with only two exceptions. 7 Tsou, Auerbach, and Wharton studied scattering of polarized LiF on Ar, without final-state selection. Treffers and Korving determined the second moment of the population distribution over m levels of scattered Na 2 molecules without initial-state selection.…”

Section: Experimental Proof Of a I Am | « J Propensity Rule In Rotatimentioning

confidence: 99%

Experimental proof of a‖Δm‖≪jpropensity rule in rotationally inelastic differential scattering

et al. 1986

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We report the first measurement of a fully state-selected (v,J it im,|) -• (v/Jf, \m f \) differential cross section in atom-molecule collisions. We have studied Na 2 -Ne, (0,6,|m/|) -(0,0,0) rotationally inelastic scattering at a collision energy of 190 meV. The data verify a pronounced |Am I « j propensity with respect to the direction of linear momentum transfer. A realistic estimate for the relative contribution of collision processes with I Am I > 0 gives an upper limit of 10%.PACS number: 34.50.Ez Significant progress has been achieved in recent years in our understanding of the detailed dynamics of such elementary molecular processes as rotationally and vibrationally inelastic collisions. 1 " 4 Despite this advance, experimental information about collisional reorientation is limited to data almost exclusively from experiments in the bulk that suffer from extensive averaging over scattering angles and directions of relative velocity.On the experimental side, advances in inelastic scattering were made possible by the development of new techniques for state-selective scattering experiments in crossed molecular beams with 1,2 and without lasers. 3 On the theoretical side, the development of the infinite-order sudden (IOS) approximation 5 had a major impact. The IOS approximation results in a decoupling of the multichannel problem, basically by virtue of the neglect of kinetic-energy change and orbital angular momentum.Excellent agreement between calculated and measured differential cross sections has been obtained. 1,6 So far, however, such comparisons have been made exclusively for cross sections that are sums over all orientations of the molecular angular momenta. There are two reasons for this. Firstly, experimental data on differential scattering of m-selected molecules were not available, with only two exceptions. 7 Tsou, Auerbach, and Wharton studied scattering of polarized LiF on Ar, without final-state selection. Treffers and Korving determined the second moment of the population distribution over m levels of scattered Na 2 molecules without initial-state selection. Secondly, the results of the IOS scattering calculations are ambiguous as far as the collisional reorientation of the molecular angular momentum is concerned. 8 It has been proposed, however, that the so-called kinematic apse, the axis parallel to the direction of linear momentum transfer Ak, is the relevant quantization axis along which the selection rule Am==0 or propensity rule |A/w| « j should hold. 9 In fact, it is easy to show, from angular momentum conservation, that Aj = RxAk is valid. 10,11 Here R is the vector from the center of the molecule to the point of contact. Obviously Aj is perpendicular to Ak and we thus have Am=0. The question arises: To what extent is this selection rule obeyed in a real system involving repulsive interaction?Although several techniques for the extraction of information about nonisotropically distributed molecular angular momenta have been described and successfully applied, 10 none of the related exper...

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Section: Experimental Proof Of a I Am | « J Propensity Rule In Rotatimentioning

confidence: 99%