The physics of grain-grain collisions and gas-grain sputtering in interstellar shocks
A. G. G. M. Tielens, C. F. McKee, C. G. Seab, D. J. Hollenbach;
ApJ, 1994, 431, 321
ABSTRACT:Grain-grain collisions and ion sputtering destroy dust grains in interstellar shocks.
An analytical theory is
developed for the propagation of shock waves in solids driven by grain-grain
collisions, which compares very favorably with detailed numerical
calculations.
This theory is used to determine the fraction of grain vaporized by a
grain-grain collision.
Our results predict much less vaporization of colliding
grains in interstellar shocks than previous estimates.
This theory can also
be used to determine the fraction of a colliding grain that melts,
shatter, or undergoes a phase transformation to a higher density phase.
In
particular, the latter two processes can be much more important in interstellar
shocks than vaporization.
The sputtering of grains by impacting gas ions is
reanalyzed based upon extensive laboratory studies and a theoretically derived
'universal'sputtering relation.
The analytical results are compared to available
experimental studies of sputtering of graphite/amorphous carbon, SiO2, SiC, Fe,
and H2O.
Sputtering yields for astrophysically relevant materials as a
function of impact energy and ion mass are derived.
These yields are also
averaged over thermal impact spectrum and simple polynomial fits to the
resulting yields as a function of temperature are presented.
The derived
sputtering yields are similar to those adopted in previous studies, except for
graphite near threshold where the new yields are much larger due to a lower
adopted binding energy.
The ion bombardment will amorphitize the surface
layers of interstellar grains.
It will also convert graphite into
hydrogenated amorphous carbon (HAC) to a depth of 10-20 A.
It is suggested that these
HAC surfaces are the carriers of the 3.4 micrometer absorption feature in
the interstellar medium.
KEYWORDS: cosmic dust, interstellar extinction, particle collisions, shock waves, astronomical models, interstellar matter, ionized gases, sputtering, wave propagation
PERSOKEY:dust, size distribution, ,
CODE: tielens94