Ian Mark Mills. 9 June 1930—23 December 2022

Ian Mills was a molecular spectroscopist who did experimental, computational and theoretical research in spectroscopy. He was particularly interested in rotational fine structure in vibrational spectroscopy, but he also made significant contributions in understanding vibrational motion itself. This included harmonic and anharmonic force fields, local modes, Fermi resonances, and large amplitude motions. He was also interested in metrology. The publication of the IUPAC Green Book on quantities, units and symbols was a very useful contribution to everybody working in physical chemistry and physics. His endeavours to redefine the kilogram, ampere, kelvin and mole by fixing the Planck constant, elementary charge, Boltzmann constant and Avogadro constant, respectively, was a major service to science.