A particle (atom or molecule) can undergo a change in its state of excitation as a
result of collisions with other particles. In an elastic collision an exchange only
of
kinetic energy takes place between the colliding species; in an
inelastic collision there is an interchange between the
kinetic energy and the
internal energy of the particle.
Source:
PAC, 1996, 68, 149
(A glossary of terms used in chemical kinetics, including reaction dynamics (IUPAC
Recommendations 1996))
on page 159