A new experimental technique which provides a laboratory environment much like that of the outer planets is described. More specifically this technique, collisional cooling, allows the study of the collisional properties of molecular species at temperatures which in ordinary spectroscopic cells would result in vanishingly small vapor pressures due to condensation. In this paper the basic theory of collisions is put forth, the experimental techniques described, and the results of pressure broadening studies for a number of species described. ¿ American Geophysical Union 1991