Question

If one wishes to examine a chemical species dissolved in aqueous solution, it is often much better to use Raman spectroscopy instead of IR spectroscopy.Predict why this might be true.

Answer 1

Raman spectroscopy is a spectroscopic technique used to observe vibrational, rotational, and other low-frequency modes in a system. Raman spectroscopy is used in chemistry to provide a structural fingerprint by which molecules can be identified.

The structural fingerprint can't be affected by the aqueous solution. Hence, Raman spectroscopy can be used to characterize the chemical species dissolved in aqueous solution.

IR spectroscopy is a spectroscopic technique, generally used to determine the functional groups present in the given molecule by measuring the vibrations of atoms.Usually, stronger bonds and light atoms will vibrate at a high stretching frequency (wavenumber).

In the case of IR spectroscopy, if you dissolve the molecule to be characterized in aqueous solution, the functional groups present in the molecule may be cleaved by hydrolysis or they form hydrogen bonding with water. As a result, IR spectroscopy is not a good technique for characterizing the chemical species dissolved in aqueous solution.

Therefore it is often much better to use Raman spectroscopy instead of IR spectroscopy for the characterization of chemical species dissolved in aqueous solution.