History of Spectroscopy

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The history of spectroscopy is a rarely told story, though it is a fascinating one that has profoundly shaped modern science. The research spans three centuries. This history takes us from age-old curiosities over the nature of light, to discoveries about the solar system and chemical elements and their structures. Although you may not know this history, you are sure to know at least some of the famous names involved.

Sitting amongst the luminaries are:

• Sir Isaac Newton - best known for his work on gravity
• Anders Jonas Ångstrom - who had the unit of measurement named after him
• Robert Bunsen - a recognisable name in all secondary high school chemistry laboratories
• Albert Einstein - quantum mechanics and the theory of relativity
• Lise Meitner - heavily involved in nuclear fission research
• Erwin Schrödinger - responsible for Schrödinger’s equation

What is Spectroscopy?

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First of all, a brief reminder on ‘What is spectroscopy?’ Spectroscopy measures the emission and absorption of electromagnetic radiation by matter. The data produced is a plot or spectrum of the emitted or absorbed energy versus the frequency or wavelength of the radiation.

Spectroscopy has been the basis for many discoveries in chemistry and physics. It is a key tool for understanding atomic and molecular phenomena, chemical structures and the nature of chemical reactions. Today spectroscopy has applications across a range of scientific and technical fields besides physics and chemistry including forensic science and medicine. Some of the main types of spectroscopic techniques are optical spectroscopy, infrared (IR) spectroscopy, ultraviolet (UV) spectroscopy, nuclear magnetic resonance, spectroscopy and more recently laser-induced breakdown spectroscopy (LIBS).

Newton’s Famous Light Experiments

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Humans have been fascinated by the appearance of rainbows since ancient times. But the phenomena remained an unexplained curiosity until Newton and his experiments with light.

In his now famous work on light and colour Newton used a prism bought from a local fair and set-up experiments at home. He darkened his chamber, letting in only a trace of sunlight through the shutter. He used the prism and split the light into a spectrum (a ‘rainbow’ of colour) upon the wall some 22 feet away.

To demonstrate the instrument itself was not producing the colour, Newton reversed the experiment by refracting the light back together again. Newton demurely announced his ‘new theory about light and colors’ in a letter (as was customary at the time) published by the Royal Society in 1672.

Newton coined the term “spectrum” and, crudely speaking, had invented the first ever spectroscope. He continued with his experiments into the nature of light and the properties of colour, later producing the book Opticks in 1704. Newton is deemed a scientific genius today but in his own day his work was contested. Likewise, the use of a prism was questioned for its status as a legitimate instrument for experimental study.

Spectroscopy In The 19th century

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A century after the publication of Optiks, natural philosophers (scientists) built upon Newton’s experiments. They used a slit rather than a rounded aperture to disperse the light. The first person to do so was W. H. Wollaston in 1802 who was followed by Joseph von Fraunhofer in 1814.

Fraunhofer introduced a convex lens between the slit and the prism and elected to view the spectral display using a telescope. With this, he had developed the first proper spectroscope. However, not all spectra were composed of coloured light. Some lines were dark and fell outside of the visible spectrum. Over 500 of these "Fraunhofer lines" were observed.

In 1859, the German physicist Gustav Kirchhoff was working at Heidelberg University alongside his friend, the chemist Robert Bunsen. The two men used Bunsen’s burner to show chemicals emit a unique kind of light when heated. Accordingly, elements and compounds each have a characteristic spectrum or "fingerprint."

Conversely, studying the spectrum of a certain material could be used the determine its chemical composition. Kirchhoff and Bunsen sought to investigate the sun’s atmosphere. The bright lines seen were obviously light coming from hot gases. But what of the dark lines? They determined these were caused by the absorption of light in the cooler gas above the sun's surface. Kirchhoff and Bunsen systematically investigated the flame spectra of salts and metals, making comparisons with the solar spectrum.

Using this process, the pair made discoveries of previously unknown elements. In 1861, Cesium and Rubidium were found. These findings were closely followed by those other researchers, who likewise made new elemental discoveries. By the close of the 1860s decade, a mysterious solar spectral line had been discovered and named helium.

A Timeline of Spectroscopy: Early 17th Century–Mid-20th Century

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A comprehensive timeline of events in the history spectroscopy features over 100 names. The history of spectroscopy thus features many places and many faces.

Here are some key highlights from its early experimental beginnings to the commercial production of spectroscopy instrumentation at the mid-twentieth century:

• 1666 – Isaac Newton conducted experiments with light and colour.

• 1786 - David Rittenhouse (American astronomer and instrument maker) produces the first primitive diffraction grating.

• 1800 - Johann Wilhelm Ritter (German chemist) discovers ultraviolet radiation

• 1802 - William Hyde Wollaston (English Scientist) observes dark line spectra of the sun.

• 1814 - Joseph von Frauenhofer (German optician) invents the transmission diffraction grating and undertakes a systematic study of dark lines in the solar spectrum. This work serves as the foundation for the science of astrophysics.

• 1826 - William Henry Fox Talbot observes that different salts produce colours when placed in a flame.

• 1859 - Gustav Robert Kirchoff (German physicist) & Robert Bunsen (German chemist) show spectral lines are unique to each element, thus founding the science of spectral analysis as a tool for studying the composition of matter.

• 1860–1861 - Kirchoff & Bunsen discover Cesium and Rubidium.

• 1868 - Pierre Janssen (French astronomer) & Joseph Norman Lockyer (English astronomer) independently discover the presence of helium in the sun through its characteristic spectral lines.

• 1868 - Anders Jonas Ångström (Swedish physicist) & Joseph Norman Lockyer (English astronomer) publishes a study of the wavelengths of solar spectral lines, expressed in units of 10^–10 meters (the angstrom Å unit).

• 1896 - Antoine Henri Becquerel (French physicist) discovers radioactivity. He shares the 1903 Nobel Prize in physics with Pierre and Marie Curie.

• 1897 - Joseph Thomson (British physicist) discovers radioactivity. He shares the 1903 Nobel Prize in physics with Pierre and Marie Curie.

• 1900 - Max Planck (German physicist) introduces the quantum concept. He is awarded the 1918 Nobel Prize in physics.

• 1905 - Albert Einstein (German physicist) explains the photoelectric effect. He receives the Nobel Prize in 1921 and publishes the "Special Theory of Relativity" the same year.

• 1913 - Niels Bohr (Danish physicist) presents a theory of the atom that explains the Rydberg formula of simple spectra. He receives the 1922 Nobel Prize in physics.

• 1923 - Louis de Broglie (German physicist) proposes the wavelike nature of the electron. He receives the Nobel Prize in physics in 1929.

• 1924 - Wolfgang Pauli formulates the exclusion principle. He is awarded the Nobel Prize 1945.

• 1925 - Pierre Victor Auger rediscovers the Auger effect (autoionization).

• 1926 - Erwin Schrödinger develops wave mechanics. He is awarded the Nobel Prize in physics in 1933.

• 1927 - Werner Heisenberg develops his uncertainty principle that explains the natural linewidth of spectral lines.

• 1937 - Maurice Hasler at Applied Research Laboratories (ARL) produces the first commercial grating spectrograph.

• 1938 - Hilger and Watts, Ltd. invent the first commercial X-ray spectrometer.

• 1955 - Alan Walsh develops atomic absorption spectroscopy (AAS).

The entirety of the cohort consists of male physicists and chemists.* Apart from just two female representatives, that is: Lise Meitner and Marie Curie.

Meitner was the first female professor in Germany, though was exiled due to the rise of the Nazis. The part she played in the discovery of nuclear fission has been mired in controversy. Meitner found herself in an unfavourable position during the wartime turbulence. This meant others were able to take credit for her work on nuclear fission.

Curie is famous for the discovery of radioactivity. Like Meitner and other women in science she was not always given due credit, though the reasons were different. In this case, scholars cited the name of Pierre (Marie’s husband) though often forgot to include Marie.

**This is not a verified fact because various first names on the list appear in the form of initials only and thus a gender cannot be ascertained.

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