Biomedical Engineering Reference
In-Depth Information
EQ
Z
1
Z
2
300
200
100
0
2
4
6
8
10
E / eV
300
200
100
0
2
4
6
8
10
E / eV
Fig. 7.2
Elastic cross sections for the five dimer geometries specified in the text, calculated with
(upper panel) the R-matrix and (lower panel) the multiple-scattering methods
between cross sections down to 0 eV for the Z
2
geometry. We observe that while
the behaviour of the R-matrix results is that expected of a cross section for electron
collisions with a non-polar molecule, the MS cross section displays the behaviour to
be expected from scattering with a polar target. We conclude that the MS treatment
is not able to properly account for the total dipole moment of the cluster when it is
very different from that of the sub-units that constitute it. It should be noted that the
agreement below 1 eV for the dimer geometry 'L', with a dipole moment more than
twice that of the isolated molecule, is much better than that for Z
2
.
The need for the
ad hoc
parameter in equation (
7.23
) mentioned in Sec-
tion
7.2.2.2
is illustrated in Fig.
7.3
. The MS cross section shows a spurious peak
for
D
D
0:75. Figure
7.3
shows the MS cross
section for both together with the
l
defined in Section
7.2.2.2
: we can see how the
spurious peak in the interpolated cross section for
1:00 that is eliminated by setting
1:00 is due to the inclusion
of
4
in the 6-8 eV range. When the thresholds for inclusion of partial waves, E
l
c
,
D
