The main effort reported is directed toward charge transfer and ionization in high energy atomic collisions. The research may be divided into classical trajectory calculations, quantum - mechanical collision theory, and phenomenological treatments of quantal interference effects in heavy ion collisions

Becker, R.L.

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Abstract for the DOE/BES Research Meeting on Hip.h Energy Atomic Physics, April 5-7, 1979THEORY OF ELECTRON TRANSFER AND IONIZATIONRichard L. BeckerOak Ridge National LaboratoryOak Ridge, Tennessee 37830TTn* *Energyport was prepared as anrd by the United Slates Covtni amliahilnv <>T rpierceri riftingdttCpi IVs not ihe Unany of then esubenni i actors,.riponsibility fmojrrf or lepresctcl \ -^wr.eJ nghed Stal•nployeeplied, ,>nmertl. Neiiheemployees, rrihf duuia>->. simple!vuik(helegal" ".....*Research sponsored by the Division of Physical Research, Department of Energyunder contract W-7405-eng-26 with Union Carbide Csrporation.By accapluncs of this snide, the publisher orrecipient acknowledges the U.S. Govanini2i>"5Mght to retain a non - exclusive, royalty - freelicense in and to any. copyright covering the3rticle, . i ^ -QE THIS DDCUMENT !S UNLIMITEDAbstract for the DOE/BES Research Meeting on High Energy Atomic Physics, April 5-7, 1979THEORY OF ELECTRON TRANSFER AND IONIZATIONRichard L. Becker, Oak Ridge National LaboratoryA small atomic theory group in the Physics Division of ORNL, formed in1977 with BES support, has had the part-time participation of staff membersJ. B. McGrory, C. Bottcher, and the author, together with the collaborationof several visitors: C. Feuillade (U. Manchester), B. R. Junker (Office ofNaval Research), K. C. Kulander (Daresbury Res. Estab.). A. D. MacKellar(U. Kentucky), and A. L. Ford and J. F. Reading (Texas A 6 M Univ.). Atpresent our research is motivated primarily by (1) needs of the magneticfusion energy program for cross sections for collision processes in plasmasand for the spectroscopy of highly stripped heavy ions, and (2) needs of de-veloping areas of atomic physics studied experimentally with charged-particleaccelerators.In the area of spectroscopy, Joe McGrory has spent some time convertingexisting nuclear shell model computer programs to a form suitable for con-figuration mixing calculations of the structure of heavy ions. Because ofcommitments in nuclear theory, he will probably not find much time to donateto atomic theory this year, and the project does not have the funding now tosupport a structure theorist. We would like very much to find a way to usethese very powerful codes for complicated atomic structure calculations.Chris Bottcher has spent part of his time in the area of chemical physicsand lasers, continuing work begun at the Univ. of Manchester.The main effort of the group has been directed toward charge transfer andionization in high energy atomic collisions. The research may be dividedinto classical trajectory calculations, quantum-mechanical collision theory,and phenomenological treatments of quantal interference effects in heavy ioncollisions.Beginning in 1964, Percival and collaborators found that the method of"molecular dynamics" (i.e. following classical trajectories starting withinitial conditions obtained by Monte-Carlo sampling) extended to electronictransitions in p+H and e+H collisions, gave results much better than those ofthe binary encounter approximation and, indeed, in good agreement with ex-periment at high impact velocities. A decade later, because of the growingavailability of multiply-charged ions, Olson and Salop did extensivePercival-type calculations for bare nuclei with Z <_ 36 incident on atomichydrogen at velocities of about 1 to 3 Bohr velocities. Partially strippedprojectile ions were also treated, in the approximation that the remainingelectrons were ignorable, by assuming a fractional effective nuclear charge.The results have been very useful, and in many cases gave good fits to ex-periments such as the ORNL charge transfer data of Phaneuf et_ al_. A gen-eralization of the calculation to treat two active electrons has been madeby MacKellar and Becker. Results for H+H collisions have been reported,and calculations are in progress for He and Li projectiles. Initial con-ditions for He and He-like ions are being sought by Becker in collaborationwith Don Noid of the Chemistry Division. Calculations for targets in Rydbergstates are also being done.Two forms of quantum mechanical theory for high energy atomic collisionsare being pursued. A modification of the Born approximation which properlytakes into account the non-orthogonality of atomic orbitals centered on dif-ferent nuclei (projectile and target) was given by Bates in 1958. The fewcalculations done so far have been rather approximate and have been restrictedby the availability of only a few two-center matrix elements containingtranslational factors. B. R. Junker, who spent the summers of 1976 and 1978Qat ORNL, has recently completed a paper on the calculation of general matrixelements of this kind and has performed some accurate Bates-Born calculationsof electron transfer. Junker and Becker are planning multi-state Bates-Bornand coupled two-center calculations.An extensive set of codes for single-center, coupled-channels calcula-tions of inner-shell vacancy production, which has been developed and used atTexas A S M University over the past several years, has been further refinedat ORNL. The codes were originally designed for direct ionization of aheavy target by a light projectile (Z >> Z ), but charge transfer to ahydrogenic ground state has been included recently. The full Hartree-Fockpotential of the target is employed and resonant virtual excitation of thecontinuum of the target (the dominant second order process) is included. A9recent calculation gives a good account of K-shell electron capture andvacancy production data of Macdcnald et̂  al_. (Kansas State U.) for high energyprotons on Ar, and preliminary calculations for 0^+ + H(q = 3 and 6) gavegood agreement with ORNL electron capture data on absolute cross sectionsand variation with ionic charge. Work in progress involves increasing theintermediate-state basis from s and p only, to s, p, and d; and incorporatingantisymmetry effects.Recent electron transfer cross sections A taken at the ORNL model ENtandem Van de Graaff accelerator with heavy projectiles, ..Ta01*, 7ylW^+, and0Au* (q = 5 to 18), incident on H atoms showed an unexpected oscillationsuperimposed on the monotonic increase with q. While we hope to account forsuch oscillations in coupled-channels calculations later, at present asimple physical explanation is called for. Bottcher has proposed (see Ref.11) a "transition state" model of capture by a highly stripped projectile athigh energies in which: first the projectile transfers energy greater thanthe ionization potential to the electron; then the electron moves classicallyto the saddle point cf the electrostatic potential where it is either capturedby the heavy ion or escapes, depending on its kinetic energy. If a is theelectron-loss cross section of binary encounter theory and a is the capturecross section, then the ratio o /at given by classical transition state theoryC L1/2is exp(-2v/q ). The oscillations in a vs. q for Z = 75 are thought toresult from an f-wave resonance in a,. Bottcher also is workinto on simpletreatments of the ratio of cross sections for molecular vs. atomic targets(e.g. H2/H) and for the forward peak in ORNL-U. Tn. data on projectile ioni-zation.References1. C. Bottcher and C. Feuillade, "Coherent Pumpint of Microwave TransitionsBetween Highly-Excited States", submitted to J. Chem. Phys.; Andrews,Baker, Bottcher, and Feuillade, "The Validity of the Few-Level Approxi-mation in Gaseous Relaxation Phenomena", ibid.2. C. Bottcher, "Excited State Potential Surfaces and Their Applications",submitted to Adv. Chem. Phys.3. C. Bottcher, "Dissociative Recombination of Large Molecular Ions", J.Phys. Bll_, 3887 (1978).4. D. Banks £t al., Computer Physics Comm. 13, 251 (1977).5. R. E. Olson and A. Salop, Phys. Rev. Al^, "531 (1977).6. R. A. Phaneuf, F. W. Meyer, and R. H. McKnight, Phys. Rev. A, 534 (1978).7. A. D. MacKellar and R. L. Becker, "Classical Trajectory Study of NeutralH Atom - H Atom Collisions", 2nd Topical Conf. on At. Processes in HighTemp. Plasmas, Boulder, Jan. 17-19, 1979.8. B. R. Junker, "Fourier Transform of Two-Center Charge Distribution"(preprint).9. A. L. Ford, J. F. Reading and R. L. Becker, "Charge Transfer and Ioni-zation in Collisions of 2.5 to 9 MeV Protons with Argon", submitted toJ. Phys. B.10. R. L. Becker, J. F. Reading, and A. L. Ford (unpbul.'shed).11. Kim, Hvelplund, Meyer, Phaneuf, Stelson, and Bottcher, Phys. Rev. Lett.40, 1635 (1978).12. Suter, Vane, Sellin, Elston, Alton, Thoe, and Laubert, Phys. Rev. Lett.41̂ , 399 (1978).

Theory of electron transfer and ionization

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Theory of electron transfer and ionization

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