A HI study of HII regions and dark clouds.

This thesis will concentrate exclusively on certain aspects of the CM. The CM is concentrated in clouds which are acted upon by radiation, cosmic rays, shock waves, gravity and the magnetic field. Although a wealth of observational material now exists concerning the CM, from HI and molecular line observations, and more recently from the IRAS survey, many questions are still unanswered. These questions concern cloud formation and evolution, the internal structure of clouds, cloud shapes, the physics of cloud boundaries, the heating agents of the CM and the role of the magnetic field. The principal aim of this thesis is to study the effects of radiation on clouds by means of HI observations, in two astrophysical contexts: 1) a molecular cloud in the interstellar radiation field (ISRF). 2) a molecular cloud exposed to dissociating radiation from nearby massive stars. ... Zie: Introduction