A semiclassical model of Rydberg atom collisions with neutral molecules that result in electron attachment has been devised and implemented as a Monte Carlo computer program. Comparisons between model calculations and experimental data have been used to investigate the reactions:$$\eqalign{&{\rm K}(n{\rm d})+{\rm SF}\sb6\to{\rm K}\sp{+}+{\rm SF}\sb6\sp{-},\cr&{\rm K}(n{\rm d})+\rm CF\sb3I\to K\sp{+}+CF\sb3I\sp{-}\to K\sp{+}+CF\sb3+I\sp-,\cr&{\rm K}(n{\rm d})+\rm CCl\sb4\to K\sp{+}+CCl\sb4\sp{-*}\to K\sp{+}+CCl\sb3+Cl\sp-.}$$These comparisons provide information about the distribution of excess energy of reaction between internal and translational degrees of freedom and about the lifetimes of the intermediate negative ions, forming the basis of one of the few techniques that can be used to measure lifetimes of collisionally produced excited species on a picosecond time scale.