Mark Child is a chemist who has made valuable contributions to the theory and interpretation of molecular collisions and molecular spectroscopy by emphasising the subtle connections between classical and quantum mechanical behaviour.

Among many achievements, his local mode theory of excited molecular vibrations provided essential insight just as the relevant states became accessible to experimental investigation. He is also well-known for a new analytical approach to the study of predissociation, the phenomenon whereby a molecule with excited electrons can dissociate into unexcited atoms without emitting radiation. More recently, he has established a reputation in the theory of molecular Rydberg states, which is designed to explain the behaviour of an excited electron as it begins to break away from the residual positive ion.

Formerly Coulson Professor of Theoretical Chemistry at the University of Oxford, Mark is currently Emeritus Professor of Theoretical Chemistry at the university. He has published several influential books, including Molecular Collision Theory (1974) and Semiclassical Mechanics with Molecular Applications (first edition 1991; second edition 2014) — the former remaining in press after 40 years.