Sydney Leach

Our eminent colleague Sydney Leach passed away on December 24, at the age of 95 years. Sydney spent his entire career (since 1946) in France at the CNRS, being one of the first “Maîtres de Recherche” of this organization. He created a new discipline, molecular photophysics, and gave this name to the laboratory he founded, at the University of Paris at Orsay, and directed for many years. This laboratory is now an important component of the Institute of Molecular Sciences in Orsay (ISMO). Sydney gave great momentum to molecular photophysics in the 60s and 70s, not only by shaping the discipline at Orsay and within France as a whole – and of course internationally too – but also by vigorously promoting the use of synchrotron radiation as a source of radiation to study molecular dynamics. Since the 1980s, his interests increasingly evolved towards astrophysical applications.

Sydney was always interested in diverse scientific areas and their interactions. His involvement in astrophysics led him to pursue the last part of his career at the Paris Observatory on its Meudon campus, in the Damap department, which has since become LERMA. Sydney, with Paul Felenbok, initiated the construction of the high-resolution 10m vacuum ultraviolet spectrograph, located in Meudon. His contributions to the study of the electronic spectra of molecules, and especially of radicals and molecular ions, are fundamental and very relevant today. He extended this field to dynamical aspects of larger species and undertook the study of fullerenes, amino acids and nucleic acids, as well as laboratory tests on the role of ions of polycyclic aromatic molecules in the interstellar medium. One of his latest projects on the international space station, EXPOSE, concerned the survival of plant seeds irradiated by UV radiation in space.

Sydney Leach was a unanimously recognized and a highly appreciated scientist: he was elected a Fellow of the Royal Society, a chevalier of the French Legion d’honneur and winner of the Robin Prize of the French Society of Physics. He was also a member of the International Astronomical Union and the National Committee of the CNRS. He was unpretentious and sensitive to others, generous and friendly, respectful to everyone. Sydney spread his impressive and broad knowledge and, thanks to his encyclopedic erudition, fostered numerous national and international collaborations in all fields of physics, chemistry, astrophysics including astrobiology.


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