Gerhard Herzberg (1980) - Spectra and Structure of Three-Atomic Hydrogen

Gerhard Herzberg (1980)

Spectra and Structure of Three-Atomic Hydrogen

Gerhard Herzberg (1980)

Spectra and Structure of Three-Atomic Hydrogen

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Some Nobel laureates receive their prizes so late in life that they let the prize mark the end of their scientific activities. Not so Gerhard Herzberg, who almost ten years after receiving the Nobel Prize in Chemistry came to Lindau with a first class scientific discovery. It is well known that two hydrogen atoms H may join into a diatomic molecule H2, but also that if a third hydrogen atom approaches the H2, it will be repelled. This seems to imply that it would be impossible to form a triatomic molecule H3. But in his lecture, Herzberg tells the fascinating story of how he and his team a few months before the Lindau meeting actually discovered H3 in their laboratory! Almost as in a section of the TV-series Forensic Files, he first states the problem, then in some detail describes the methods to be used and finally solves the problem using the technical equipment of his laboratory. The story starts with a slightly simpler molecule, the electrically charged ion H3+. Traces of this molecular ion were seen in the laboratory already in the early 1900’s by Nobel laureate J.J. Thomson and later on in different kinds of particle accelerators. But it wasn’t until almost 90 years later that the important discovery was made by Takeshi Oka, a colleague of Herzberg, that this ion is abundant in space, where it plays an important role in the interstellar media. There it may meet an electron e- and form a loosely bound so-called Rydberg system (H3+ + e-). But this is just the molecule H3, even if it doesn’t appear in its lowest energy state. Precisely this process was found in Herzberg’s laboratory just before he came to Lindau. He ends his lecture by mentioning the process dissociative recombination, which describes the formation an decay of the Rydberg system. Interestingly enough, the details of the formation and decay of H3 has now been studied in detail in accelerator experiments starting only a few years after Herzbergs discovery.

Anders Bárány

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