The mechanism of energy transfer in H2O–H2O collisions – a molecular dynamics simulation Original Research Article

Earlier work on the activation-deactivation mechanism of gas phase unimolecular reactions is extended to the study of the detailed energy transfer mechanism in collisions of water molecules. Molecular dynamics simulations of binary collisions between a reactant water molecule at high internal energy with medium molecules at various selected initial temperatures are compared with results from approximate statistical theory. Energy transfer is related to (i) interaction strength, (ii) hard atom–atom encounters, (iii) multiple minima in the center of mass separation, (iv) collision lifetime and (v) anharmonicity of the intramolecular potential function. The observed trends are interpreted within the framework of the partially ergodic multiple encounter theory (PEMET) of collisional energy transfer. By comparison with typical stable molecule collisions the water–water collisions are more efficient as a reflection of the strong hydrogen bonding interactions. A good agreement between PEMET and molecular dynamics simulations over a wide range of interaction strengths and initial reactant energies is shown, indicating the possibility of a priori use of the PEMET model.