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Fellows Directory

Ian Mills

Ian Mills

Professor Ian Mills OBE FRS


Elected: 1996


Ian Mills was recognised for his experimental observation and theoretical analysis of high-resolution rotation, vibration-rotation and electronic-vibration-rotation spectra of small molecules, with emphasis on determining potential energy surfaces and dipole moment functions. He developed least squares refinement schemes to obtain harmonic and anharmonic force fields through perturbation theory and variation theory. He also contributed to our understanding of local mode effects in highly excited vibrational states.

Later, Ian played a leading role in developing both the language of science and the International System of Units (the SI). He led the current revision of the SI so that it is based exclusively on the fundamental constants of physics (for example, c, h, e, k, and NA) in place of international prototypes such as the prototype kilogram. He edited the definitive IUPAC volume Quantities, Units and Symbols in Physical Chemistry, and successive editions of the SI Brochure, published by the Bureau International des Poids et Mesures. In recognition of this he was awarded an OBE in 2015.

Professor Ian Mills OBE FRS died on 23 December 2022.

Professional positions

Emeritus Professor of Chemical Spectroscopy, School Of Chemistry, University of Reading
Emeritus President of the CCU, Bureau Internationale des Poids et Mesures

Interest and expertise

Subject groups

  • Astronomy and physics
    • Quantum theory
  • Other
    • Other interests, History of science
  • Chemistry
    • Chemistry, theoretical


molecular spectroscopy, the language of science, metrology

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