Caren Sullivan–April 8th, 2016

Unfortunately, the LabSpec software is not currently communicating with the electronics of the Raman/confocal microscope. We have emailed JY Horiba and are waiting on a response; until then, I am unable to take spectra. I have spent some time this week brushing up on how Raman spectroscopy works, particularly for my senior experience talk.

When a molecule absorbs energy, but less energy than that required to promote an electron to an excited electronic state, a virtual excited state is created. Then, the majority of the light absorbed is emitted 360 degrees around the molecule and at the same energy as the incident light. This is called Rayleigh scattering. However, a very small fraction of the light is emitted at either a higher or lower energy than the incident light. This is called Raman scattering. An emission of light of a higher energy occurs due to a loss of vibrational energy; an emission of light of a lower energy occurs due to a vibrational promotion. Due to the dense population of electrons in the ground state, the latter (emission of lower energy) is more likely to occur. This is called Stokes scattering (and emission at a higher energy is called anti-Stokes).

In order for a molecule to be Raman active, there must be a change in the polarizability (or distortion of the electron cloud) during vibration (caused by the incident light). On the other hand, IR spectroscopy requires an electric dipole moment. Due to the fact that a molecule that experiences a change in the polarizability will not experience an electric dipole moment, and vice versa, Raman and IR compliment each other.

Ultimately, this review of Raman spectroscopy will serve as a nice introduction to my senior experience talk. However, I hope the Raman is up and working again soon such that I can begin taking spectra again!

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