David Smith. 26 November 1935 — 15 February 2023

David Smith was an exceptional chemical physicist who greatly contributed to the field of molecular science by inventing novel techniques and instruments to study gas-phase reactions of electrons and ions. These reactions are important for understanding the atmospheres and interstellar media. One of his inventions was the flowing afterglow Langmuir probe apparatus, which was used to collect data on electron attachment and electron–ion recombination. Another technique he developed was the selected ion flow tube (SIFT), which helped to understand thousands of ion–molecule reactions. This innovative technique has become the foundation of a new analytical method called SIFT-MS, which is currently used in various industries such as semiconductors and pharmaceuticals, as well as in biological and medical research.