Biomedical Engineering Reference
In-Depth Information
300
MS
MS 'trimmed'
Gianturco et al. (2005)
250
200
150
100
1
2
3
4
5
6
7
E / eV
Fig. 7.5
Elastic cross section for (HCOOH)
2
collision, calculated with the Multiple Scattering
method and
1:25; the monomer data was generated using a static-exchange plus polarization
model. Comparison with prior calculations [
6
] is shown; the arrows indicate where the two shape
resonances are experimentally found [
30
]
D
study how well the multiple-scattering technique is able to reproduce the presence
of resonances in a collisional process.
The characteristics of the R-matrix calculations performed in order to obtain the
monomer input for the MS calculations can be found elsewhere [
34
]. The model,
in this case, was chosen so as to best represent a shape resonance present in the
1.4-2.0 eV range (see [
35
] and references therein) in electron-HCOOH scattering.
The formic acid dimer is rich in resonances: Gianturco and collaborators [
6
] identify
seven in the energy range up to 15 eV. The two lowest have also been observed by
Allan [
30
] at 1.4 and 1.96 eV: they can be interpreted as originating from the split of
the monomer resonance mentioned above. It is these two resonances that we expect
the MS technique to be able to represent.
Figure
7.5
shows the MS cross section for (HCOOH)
2
: for this system, the use
of 'trimmed' monomer T-matrices (see Sect.
7.2.2.2
) produces a cross section that
is visibly different to the one generated from 'correct' T-matrices. Both of them
display a peak centred around 1.45 eV, but the second peak appears at different
energies: using the 'trimmed' T-matrices produces a peak centred around 1.7 eV
whereas the latter calculation produces a smaller peak centred around 1.83 eV, in
better agreement with experimental results. Calculations with other models also
show the presence of two peaks in the low energy region. Notice that for this system
and model,
1:25 was required. We conclude that the MS technique is able to
reproduce the presence of two resonances.
D
