Karl Ferdinand Herzfeld (February 24, 1892 – June 3, 1978) was an Austrian–American physicist and chemist. He worked on condensed matter physics, fluid dynamics, reaction rate theory, and statistical mechanics. In seminal 1919 and 1921 papers, he derived the rate equation for unimolecular reactions and proposed the Lindemann mechanism of third-body deactivation in unimolecular reactions. In 1927, he was the first to quantify when a substance is a metal or an insulator. The Goldhammer–Herzfeld criterion to classify metalloids is named after him. Herzfeld and Frank O. Rice developed the theory of translational-vibrational energy transfer, and proposed the radical mechanism for pyrolysis in 1934, known as the Rice–Herzfeld mechanism. Herzfeld also wrote on philosophy and theology. He was married to anthropologist Regina Flannery.
Education Karl Ferdinand Herzfeld was born on February 24, 1892, in Vienna, into a "prominent, recently assimilated Jewish family". His father was Professor Ordinarius of Obstetrics and Gynecology at the University of Vienna. His mother, Camilla Herzog, was the daughter of a newspaper publisher and sister of the organic chemist R. O. Herzog. In 1902, Herzfeld enrolled at the Schottengymnasium. He attended the school until 1910, when he entered the University of Vienna to study physics and chemistry. In 1912, he took courses at the University of Zurich and ETH Zurich. It was at ETH that he met Otto Stern; Herzfeld later credited conversations with Stern for his deeper understanding of thermodynamics. In 1913, Herzfeld went to study at the University of Göttingen, after which he returned to Vienna and received his Ph.D. the following year under Friedrich Hasenöhrl, who had become director of the Institute for Theoretical Physics upon the suicide of Ludwig Boltzmann in 1906. Herzfeld's thesis applied statistical mechanics to a gas of free electrons as a model for a theory of metals. By the time he received his doctorate, he already had published six scientific papers. In one of them, he attempted to derive a model of the hydrogen atom. This paper was published in 1912, shortly before Niels Bohr submitted his first paper on the Bohr model of the hydrogen atom. Upon receipt of his doctorate, Herzfeld volunteered for service in the Austro-Hungarian Army. World War I broke out shortly thereafter and he served until 1918, rising to the rank of first lieutenant. Herzfeld's thesis advisor Hasenöhrl was called to serve during World War I and was killed at the front. During his tenure in the military, Herzfeld published six papers on statistical mechanics applied to problems in physics and chemistry, especially to the structure of matter – gases, liquids, and solids.
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