ELFT HÍRADÓ

[Zoltan Mate <mate AT atomki.mta.hu>]

Az MTA Atommagkutató Intézetének előadótermében
(Debrecen, Bem tér 18/c. 12. ép. III. em.)
2012. május 22-én, KEDDEN 14:00-kor


               Jonathan Tennyson
           (University College London)

      Positron and electron molecule collision
           calculations using the R-matrix


címmel előadást tart.
Az előadás előtt 13:30-tól tea, vendégeket szívesen látunk.


                                           Máté Zoltán


Kivonat:

The R-matrix method is based on the division of space into two
regions: a sphere which contains the  wavefunction and outer
region in which only long-range interactions between the target and the
projectile need to be considered. The method has been widely used to study
electron atom and molecule collisions at low colliison energies, those 
below the target ionisation threshold.

My group has developed a molecular R-matrix  with pseudostates method
(RMPS) which can be used to extend collision calculations to
intertermediate energies and provide, for example, an ab initio
treatment of electron impact ionisation. The ability of the RMPS
method to give a converged representation of polarisation means that
it has become the method of choice for treating problems where 
polarisation effects are important.

The method has been used to successfully treat electron collisions
with the lithium dimer, the most polarisable small molecule known. 
RMPS studies of electron collisions with small molecular anions
showed that the observed  quasibound states are due to strong
polarisation effects which overcome the Coulomb repulsion between
the two extra electrons. 

Recently the RMPS method has been applied to the challenging problem
of low-energy positron molecule collisions where the repulsive static 
potential counteracts attractive polarisation forces, making it hard to 
obtain physically reasonable cross sections using standard scattering
models. RMPS calculations resolve this issue provided pseudostates with 
high angular momentum are included in the model.
The method also gives good results for the calculation of Zeff, the
parameter used to represent annihilation in positron molecule
collisions.  This parameter constitutes the most stringent test of
any low-energy positron collision model; RMPS Zeff are a major
improvement over simpler R-matrix models.

Sample results of both electron and positron collisions calculations
will be given.