Extremely high resolution infrared diode lasers have been employed to study fundamental collision dynamics. High energy molecules, produced by excimer laser photolysis, are used as reagents to investigate collisional excitation of individual rotational and vibrational states of molecules. Translational energy recoil of the target molecules is probed by measuring the time dependent Doppler profile of the molecular infrared transitions. Quenching of highly vibrationally excited molecules such as C6F6, pyrazine, and methyl pyrazine having chemically significant amounts of energy (50-100 Kcal/mole) has been studied by observing the uptake of energy by a small bath molecule such as CO2 on a single collision time scale. Two kinds of mechanisms, involving both soft and hard collisions, are observed in which the energy transferred in the collision is large (DE>>kT). Soft collisions excite stiff, high frequency modes of the bath, while hard collisions are responsible for significant translational and rotational excitation. In addition the data can be inverted to produce the energy transfer distribution function P(E,E'). P(E,E') is the normalized probability that a donor molecule with initial internal vibrational energy E' will lose DE=E'-E during a collision, ending up with a new internal vibrational energy E. 00-8000 cm-1 have been obtained. Fits of the data to distribution functions with at least two exponential fall offs have also been made. Significant differences have been observed among the P(E,E') functions for molecules with a preponderance of low frequency vibrational modes versus molecules with a number of high frequency C-H stretching modes.