We propose to observe the interaction of X-rays from young stars in
molecular clouds with the surrounding dust. For T Tauri stars in
the outer regions of molecular clouds, the signature of this
interaction is predicted to be the disappearance of PAH features
within 0.01 to 0.1 pc from the star. For Herbig Ae/Be stars, which
are usually surrounded by dense circumstellar dust, the signature
of X-ray interaction may be the disappearance of PAH emission in
the close vicinity of the star. From recent X-ray data provided by
the ROSAT and ASCA satellites, we select 4 T Tauri stars in the Rho
Oph cloud (autumn launch), and 3 in the Orion and Taurus clouds
(spring launch). We also select 6 Herbig Ae/Be stars with a wide
range of X-ray luminosities. We use the imaging properties of
ISOCAM (using 7 filters centered on PAH and silicate features and
their references) to study the dependence of the PAH emission as a
function of distance to the X-ray source. The results should
constrain both our knowledge of the composition of the smallest
dust grains, and of the heating of dust by hard radiation.