Gerhard Herzberg

Physical Chemistry

Won the 1971 Nobel Prize in chemistry for using spectroscopy to discover the internal geometry and energy states in simple molecules, and in particular the structure and characteristics of free radicals.

"You shouldn’t do science just to improve wealth — do science for the sake of human culture and knowledge. There must be some purpose in life that is higher than just surviving."

Herzberg was a physicist, but his discoveries are important to chemists because they involve the internal geometry and energy states of molecules. Remember: When Herzberg was born, the concept of an electron was just catching on. When he graduated from university, people had yet to discover how atoms combined to form molecules. It was all new theory. Very little had been proven.

To try to prove all these exciting ideas, Herzberg became a pioneer in the field of molecular spectroscopy, the study of how atoms and molecules emit or absorb light. By analyzing spectrograms — a sort of photograph of the way a molecule emits and absorbs light — he was able to tell a lot about molecules. For example, by measuring the distance between the lines on a spectrogram and counting how many lines there were, he was able to apply some mathematical formulas that described the energy levels and probable locations of the electrons in the molecule. This was very useful to chemists, because the new knowledge helped them to imagine new ways to combine chemicals to create new substances.

Once the spectrum of a molecule is known, astronomers can also use it. They can characterize the composition of distant stars and nebulae by training spectrographs on them through telescopes. This is handy if you are interested in knowing what stars are made of. It’s a way to learn what is out there, millions of light years away, without having to make the impossibly long trip to visit a place and take samples. This is one thing that really interested Herzberg, because it tied in with his childhood love of astronomy.

A spectrogram is created with a machine called a spectrograph. It takes a beam of light created by burning the chemical you wish to investigate. The light is focused by a lens, then passed through a prism and spread out into its component parts, like a rainbow. But this rainbow is very precise and appears as dark and light vertical lines that you can measure.

A spectrogram is a long piece of plate glass coated with photographic chemicals. After they have been exposed in a spectrograph and developed, the plates have dark, vertical lines. By measuring the spacing and thickness of the lines, physicists can apply mathematical formulas and determine some of the energy states of the molecules whose light produced the spectrogram.

The distance between the larger lines in the spectrum is proportional to the molecule’s “vibrational” energy. The small groups of lines clustered around the major lines represent the “rotational” energy of the molecule. These lines and their mathematical relationships are called Balmer lines, for the Swiss high school teacher who figured them out in 1885.

Methylene (CH2) is a free radical, which means it has an extra pair of electrons that it tries to share with another molecule. These extra electrons make the free radical very reactive, meaning it will combine quickly, usually within a few millionths of a second, with some other molecule.


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MYSTERY

Strange as it may seem, in his later years Herzberg liked to remind people that they should not do science for the purpose of doing something useful. “That’s not why I did it,” he said. “Scientists wonder how certain things work, so they try more and more to find out how and why. Whether or not their work will lead to something useful, they don’t care, because they don’t know, and for that matter, they’re not that interested. If you develop science only with the idea to do something useful, then your chances of discovering something useful are less than if you apply your mind to finding something essential.” According to Herzberg, a true scientist looks to uncover the mysteries of nature for the sole purpose of advancing human knowledge. The usefulness of this knowledge becomes self-evident after it is discovered. Prime examples of this are X-rays and lasers, both of which were discovered by physicists who had no idea how useful their discoveries would later become.

Explore Further

Gerhard Herzberg, Atomic Spectra and Atomic Structure, Dover, 1944.

J. Michael Hollas, Basic Atomic and Molecular Spectroscopy, Wiley-RSC, 2002.

Boris Stoicheff, Gerhard Herzberg: An Illustrious Life in Science, NRC Press, McGill-Queen’s University Press, 2003.

An introduction to spectroscopy on the NASA Goddard Space Flight Center website.

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