John Milton Brown

Abstract John Milton Brown began his independent scientific career at the University of Southampton in 1971 and moved to the University of Oxford some 12 years later. His interests centred on the measurement and interpretation of the spectra of small free radicals (generally unstable, open-shell species with one or more unpaired electrons) in the gas phase. John's achievements in this field earned him international renown and led to many collaborations with leading overseas spectroscopists. Theoretically, he was recognized for his development of Hamiltonian-based models for interpreting the fine structure evident in the pure rotational, the rovibrational and the rovibronic spectra of such open-shell species. Experimentally, John was in the vanguard of those applying laser magnetic resonance spectroscopy and, latterly, visible laser induced fluorescence methods to the measurement of high-resolution spectra of many free radicals, including species such as CH, OH, SiH, and small, metal-containing species, such as CuCl, TiO and FeH. Knowing and understanding the spectroscopy (and thus the pattern of the energy levels) of such species is crucial, given our increasing ability to record spectra from different regions of the interstellar medium. The relative intensities of lines in the spectra of such species are one of the most incisive reporters of the conditions prevailing in the region under observation. John is remembered as a courteous, collaborative and rather humble scientist, with great professional integrity. His achievements in his chosen field—high-resolution free radical molecular spectroscopy—will underpin and inform scientific progress in many other fields of endeavour for many years to come.