A study of ultra-low-energy electron-molecule collisions using very-high-n Rydberg atoms

[摘要] In the present work very-high-n Rydberg-atoms $(n sim 100 - n sim 400)$ are used to probe electron-molecule collisions at ultra-low electron energies. Based on the essentially-free-electron model, for sufficiently high n, Rydberg atom-molecule collisions can be described in terms of a binary interaction between the target molecule and the essentially-free Rydberg electron. Since the average kinetic energy of the Rydberg electron is ultra-low $m({sim}85mu eV - {sim}1.4meV),$ analysis of the very-high-n Rydberg-atom collision data can provide information on electron-molecule scattering at electron energies corresponding to electron temperatures of only $sim$1$spcirc$K, which are far below those accessible using any alternate approach.Rate constants for destruction of very-high-n Rydberg atoms in collisions with various target molecules have been measured. This study focuses on Rydberg electron transfer to an electron-attaching molecule which results in negative ion formation via the reactions $$m K({it np/}) + XY o Ksp+ + (XY)sp{-*} or o Ksp+ + Xsp- + Yeqno(1)$$and on rotational energy transfer from polar molecules which leads to Rydberg atom ionization $$m K({it np/}) + XY({it J/}) o Ksp+ + {it e}sp- + XY({it J/}-1)eqno(2)$$The n dependence of the rate constants for Rydberg-atom destruction depends on the reactions involved. In reaction (1) the rate constant is independent of n whereas in reaction (2) it increases nearly linearly with n. When both reactions are possible, the measured n dependence can be explained in terms of contributions from each process.The essentially-free-electron model suggests that the n dependence of the rate constants for Rydberg-atom destruction reflects the energy dependence of the cross sections of the corresponding free electron-molecule collision processes which are $$eqalignno{&esp- + m XY o (XY)sp{-*} or o Xsp- + Y&(1spprime)cr &esp- + m XY({it J/}) o {it e}sp- + XY({it J/}-1)&(2spprime)cr}$$Analysis of the data therefore provides the behavior of cross sections for these processes at ultra-low electron energies.

[发布机构] Rice University

[效力级别] physics