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Who said: “A change in motion is proportional to the motive force impressed and takes place along the straight line in which that force is impressed.”
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Thumbnail of Dudley R. Herschbach (source)
Dudley R. Herschbach
(18 Jun 1932 - )

American chemist and educator who pioneered the use of molecular beams to investigate the processes of chemical reactions.

Dudley R. Herschbach

Dudley Herschbach
Dudley Herschbach (source)

Dudley Robert Herschbach was born 18 June 1932 in San Jose, California. He began his university education at Stanford University, then earned a Ph.D. in Chemical Physics (1958) at Harvard University. Herschbach then joined the Chemistry Faculty at the University of California, Berkeley (1959-1963), before returning to his alma mater, Harvard University as Professor of Chemistry (1963), where he became Baird Professor of Science (1976).

He developed the method of crossed molecular beams, directed and well-defined fluxes of molecules, to and beyond the point where detailed studies of chemical reactions have been possible. Working with others, he elucidated the mechanisms of chemical reactions, detailing the sequence of events and energy release.

Prior to his work, any fundamental understanding of what molecular features influence the rate of chemical reactions had been slow in developing. Whether a chemical reaction takes place, the colliding molecules often requires some special property such as high velocity or large internal energy. However, the directions and velocities of the molecular motion in a gas or a liquid are mainly random. Consequently, the collisions between the molecules are ill-defined as regards, for example, the kinetic energy in the collision. The details of the reaction thus become blurred and cannot be observed precisely enough.

Diagram showing idealized molecular beams crossing. Oxygen and hydrogen atoms form an unstable complex which dissociates.
Two directed molecular fluxes are shown (idealized molecular beams). Where they cross, a reaction can take place and new molecules can form. In this example, oxygen atoms (red) react with hydrogen molecules (black), and form a long-lived complex, which is an energy-rich and thus unstable water molecule. Each complex dissociates finally to a hydrogen atom and a hydroxyl radical (departing top left). (source)

In 1959 Herschbach found It was finally found possible to solve the problem by using molecular beams formed of directed and spatially well-defined molecular fluxes of low density, often also with well-defined velocities, rotational and vibrational energies. When two molecular beams are caused to cross each other, the details of the reactions between molecules can be studied from the angular distribution of the products from the point of collision, and their rotational and vibrational energies.

Herschbach first used this technique to study the chemical reaction between potassium atoms and methyl iodide molecules. The crossed molecular beam technique has since become one of the most important advances within the field of reaction dynamics, with others advancing the experimental applications in other systems (Yuan T. Lee).

He took part in the development of this method almost from the start. His extremely important achievements concerned for example studies of short-lived direct reactions, especially of the two main types, the “rebound” and the “stripping” reaction. He supplemented the commonly-used procedure of detecting the product molecules by deflecting them in magnetic and electric fields, thus circumventing one of the largely-overlooked problems inherent in the early experiments.

Professor Herschbach has published over 350 research papers. The research of Professor Dudley Herschbach and his group aims to elucidate the molecular dynamics of chemical reactions and the underlying forces, both in single-collisions and in condensed phases. Currently, his research is devoted to molecular beam studies of reaction stereodynamics, intermolecular forces in liquids and a dimensional scaling approach to electronic structure.


See also:

Nature bears long with those who wrong her. She is patient under abuse. But when abuse has gone too far, when the time of reckoning finally comes, she is equally slow to be appeased and to turn away her wrath. (1882) -- Nathaniel Egleston, who was writing then about deforestation, but speaks equally well about the danger of climate change today.
Carl Sagan Thumbnail Carl Sagan: In science it often happens that scientists say, 'You know that's a really good argument; my position is mistaken,' and then they would actually change their minds and you never hear that old view from them again. They really do it. It doesn't happen as often as it should, because scientists are human and change is sometimes painful. But it happens every day. I cannot recall the last time something like that happened in politics or religion. (1987) ...(more by Sagan)

Albert Einstein: I used to wonder how it comes about that the electron is negative. Negative-positive—these are perfectly symmetric in physics. There is no reason whatever to prefer one to the other. Then why is the electron negative? I thought about this for a long time and at last all I could think was “It won the fight!” ...(more by Einstein)

Richard Feynman: It is the facts that matter, not the proofs. Physics can progress without the proofs, but we can't go on without the facts ... if the facts are right, then the proofs are a matter of playing around with the algebra correctly. ...(more by Feynman)
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