Bunsen Burner trumped Spectropolarimetry – a fiery anecdote

December 27, 2018 by Chetana Badala Viswanatha

When the electric field vibrations of ordinary light are restricted in some manner, we obtain polarised light. In plane polarised light, the electric field oscillates in one direction only. Molecules which cannot be superposed on their mirror images can rotate this plane of polarisation. This property is known as optical activity. Optical activity is dependent on the wavelength of light. A so-called optical rotatory dispersion curve, which represents this dependency, is obtained by a technique called spectropolarimetry. The optical rotatory dispersion curve was already discovered at the beginning of the 1800s. This knowledge remained with select few physicists and chemists until the mid-20th century. Spectropolarimetry remained stagnant for over a hundred years!

So how did the Bunsen burner delay the development of spectropolarimetry?

Most school students are familiar with the flame test. If one holds a piece of rock salt in the flame, it is easy to produce yellow light which is nearly monochromatic i.e. of single wavelength. This was sufficient for the scientists studying optical activity and attention was drawn away from spectropolarimetry. Scientific applications were limited (stereochemical problems) and their requirements were satisfied by one wavelength alone. In 1953, spectropolarimetry was finally revived by Carl Djerassi. (https://doi.org/10.1002/anie.196800141)

Post written by Chetana Badala Viswanatha

Chetana Badala Viswanatha (Chetana B V) is a freelance science communicator with a passion for science writing. She holds a Master's degree with a specialization in Quantum Chemistry from RUB, Germany. She is currently pursuing a PhD in Experimental Physics at TUK, Germany. Her master thesis work on the theoretical calculation of circularly polarized phosphorescence is published (DOI: 10.1039/C8CP03385D) in the 2018 PCCP HOT Articles. She believes in crisp and simple explanation of scientific concepts.

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