Introduction to electron-molecule collision

The process of electron-molecule scattering can be described by:

    elastic scattering

   inelastic excitationionization (dissociation)

文本框: Fig. 1

These processes extensively exist in the atmosphere, nuclear fusion confined by magnetic field or inertia and gases discharge. Therefore, the data of cross sections and oscillator strengths for electron-molecule impact are significant not only for the development of atomic and molecular physics but also for the advancement of astrophysics, plasmas physics, confined nuclear fusion, X-ray laser and the safety of aerocraft.


文本框: Fig. 2


The accurate measurement of oscillator strength is always one of the most important contents for electron-molecule impact, and this kind of data have already been extensively used in astrophysics [1, 2]. For example, the Hubble Space Telescope (Fig. 1) and space satellites have observed a number of spectra for different interstellar clouds (Fig. 2), and from these spectra the information of element constituents can be determined. In this procedure, the data of absolute oscillator strengths and cross sections must be used, and large numbers of data are provided by the experiment of electron-molecule impact [1]. We know that carbon monoxide is the second most abundant molecule, after H2, in interstellar clouds. In diffuse clouds, the amount of CO is mainly derived from measurements of absorption at UV wavelengths. But due to the inaccuracy of the data measured by early experiments, the observed spectra are hard to be explained. However, the recently measured oscillator strengths by electron impact have resolved this problem, and the measured spectra for the stars  Ophiuchi A and  have been well simulated [1].

The data of cross sections also have significant application in planet science. For example, of all of the fascinating questions in contemporary astrophysics, those relating to the origin and formation of the solar system must rank high in the curiosity of everyone. Cometsoften lumped in texts under the heading ‘solar system debris’, are pursued because their chemical composition holds unique clues to the early history of our solar system, this is accessible by analyzing its constitute [3].

Another application of the cross-section data determined by electron impact is the gases discharge process, which is directly related to the development of applied techniques such as laser, plasma deposition and etching of semiconductors, and plasma display [4]. Our everyday life is benefited from this great progresses of these techniques [Fig. 4].

In order to obtain the differential cross sections and oscillator strengths of electron-molecule impact, the energy dispersion and angular distribution of scattering electron intensity should be determined and this can be achieved by electron-energy-loss spectrometer. In recent years, the important progresses in experiment technique are: (1) the progress of relatively flux technique [4]; (2) the experimental realization of high energy resolution [5]; (3) the spread of multi-channel measurement [6]; (4) the development of preparation technique of excitation target [7]; (5) the realization of the large angular measurement technique [8] and so on. The accuracy and extent of experimental data are greatly improved with the progresses of these experimental techniques. With the progress of the experiment technique, there will be more development for electron-molecule impact, and the data will be also updated constantly.


[1]     S. R. Federman , D. L. Lambert, J. Electro. Spec. Relat. Phenom., 123, 161(2002)

[2]     B. L. Rachford et al., Astrophys. J. 555, 839(2001)

[3]     M. J. Mumma, H. A. Weaver, H. P. Larson, M. Williams and D. S. Davis, Science 232, 1523(1986)

[4]     M. J. Brunger and S. J. Buckman, Phys. Rep. 357, 215(2002) and the references therein

[5]     G. Knoth, M. Gote, M. Radle, K. Jung and H. Ehrhardt, Phys. Rev. Lett. 62, 1735 (1989)

[6]     X. J. Liu, L. F. Zhu, X. M. Jiang, Z. S. Yuan, B. Cai, X. J. Chen and K. Z. Xu, Rev. Sci. Instrum., 72,3357-3361(2001)

[7]     S. Trajmar and J. C. Nickel, Adv. At. Mol. Opt. Phys. 30, 5(1992)

[8]     F. H. Read and J. M. Channing, Rev. Sci. Instrum. 67, 2372(1996)