126
M.C. Bacchus-Montabonel
Fig. 6.4 Semiclassical (blue)
and wave packet (red) partial
and total cross sections for
the CS + molecular system in
the 0.5–50 eV E CM energy
range: doublet manifold (full
lines); quartet manifold
(dashed lines); total cross
section (full lines)
Table 6.2 Rate coefficients
for the C + + S reaction (in
cm 3 s −1 )
T (K)
C + ( 2 P) + S( 3 P) → C( 3 P) + S + ( 4 S)
Semiclassical dynamics
Quantum dynamics
10
6.0 × 10 −12
50
1.3 × 10 −11
100
1.9 × 10 −11
500
1.8 × 10 −11
4.1 × 10 −11
1000
3.8 × 10 −11
5.6 × 10 −11
5000
7.3 × 10 −11
9.0 × 10 −11
10000
7.3 × 10 −11
1.0 × 10 −10
50000
1.3 × 10 −10
1.5 × 10 −10
total cross section remains close in wave packet and semiclassical approaches, even
at eV energies. Such a result is very encouraging in order to have, at a low price,
an order of magnitude of cross sections, and consequently rate coefficients, for a
number of astrophysical processes.
This is visualized on the corresponding rate constants presented in Table 6.2
using, on one hand, the semi-classical cross sections, and, on the other hand, the
wave packet quantum approach. Integration over the whole collision energy domain
down to 10 −3 eV for the quantum dynamics may provide charge transfer rate constants at low temperature. This is of course not possible with semiclassical methods
for which rate constants cannot be established for temperatures lower than 500 K.
However, such semiclassical approaches may provide the correct order of magnitude, in particular at higher temperatures. The absolute values are significantly lower
than the 1.5 × 10 −9 cm 3 s −1 rate constant given in the UMIST data base for the
10–41000 K temperature range, in particular at low temperature. The variation is
relatively smooth, between about 10 −11 –10 −10 cm 3 s −1 , which could be in relative
accordance with the constant rate considered in astrophysical models, but the usual
value seems to be overestimated at least by a power of 10.
M.C. Bacchus-Montabonel
Fig. 6.4 Semiclassical (blue)
and wave packet (red) partial
and total cross sections for
the CS + molecular system in
the 0.5–50 eV E CM energy
range: doublet manifold (full
lines); quartet manifold
(dashed lines); total cross
section (full lines)
Table 6.2 Rate coefficients
for the C + + S reaction (in
cm 3 s −1 )
T (K)
C + ( 2 P) + S( 3 P) → C( 3 P) + S + ( 4 S)
Semiclassical dynamics
Quantum dynamics
10
6.0 × 10 −12
50
1.3 × 10 −11
100
1.9 × 10 −11
500
1.8 × 10 −11
4.1 × 10 −11
1000
3.8 × 10 −11
5.6 × 10 −11
5000
7.3 × 10 −11
9.0 × 10 −11
10000
7.3 × 10 −11
1.0 × 10 −10
50000
1.3 × 10 −10
1.5 × 10 −10
total cross section remains close in wave packet and semiclassical approaches, even
at eV energies. Such a result is very encouraging in order to have, at a low price,
an order of magnitude of cross sections, and consequently rate coefficients, for a
number of astrophysical processes.
This is visualized on the corresponding rate constants presented in Table 6.2
using, on one hand, the semi-classical cross sections, and, on the other hand, the
wave packet quantum approach. Integration over the whole collision energy domain
down to 10 −3 eV for the quantum dynamics may provide charge transfer rate constants at low temperature. This is of course not possible with semiclassical methods
for which rate constants cannot be established for temperatures lower than 500 K.
However, such semiclassical approaches may provide the correct order of magnitude, in particular at higher temperatures. The absolute values are significantly lower
than the 1.5 × 10 −9 cm 3 s −1 rate constant given in the UMIST data base for the
10–41000 K temperature range, in particular at low temperature. The variation is
relatively smooth, between about 10 −11 –10 −10 cm 3 s −1 , which could be in relative
accordance with the constant rate considered in astrophysical models, but the usual
value seems to be overestimated at least by a power of 10.