Measurement - IR and Raman Spectroscopy

What is a Perrin-Jablonski diagram?

a diagram that showcases differences in absorption, fluorescence, and phosphorescence (helpful for any kind of spectroscopy)

What is vibrational spectroscopy?

assessing vibrations due to atomic bonds - you can characterize a molecule based on its response to vibration, due to the nature of atomic bonds

How does linearity affect vibrational spectroscopy?

non-linear molecules have more frequent vibrations than the same molecular structure that’s linear (partially due to resonance of electrons)

What are group frequencies?

double/triple bonds or heavy atoms will have distinct vibrational frequencies, regardless of what these are bonded to

NOT in all molecules

Advantage of IR spectroscopy?

high throughput, simple to use, good with analytical chemistry

MAJOR problem with IR spectroscopy (think biology)

Can’t handle water at all, disallowing for aqueous solution if one wishes to use it

Difference between IR spectroscopy and Raman spectroscopy?

Both use infrared, but Raman is looking at scattering from the photon’s effect. In IR, you are looking at effect of SINGLE photon as it bounces, so imagine ½ the data to collect compared to Raman

Stokes vs Anti-Stokes photons?

Stokes photons are hitting the particle and losing energy on the scatter, giving you peaks at a lower number of energy

Anti-stokes photons hit an excited photon and thus have a net energy gain

Describe the relationship between Stokes and Anti-Stokes photons’ final wavelength

They are identical but on opposite sides of zero. Anti-Stokes’ are negative wavelength with a value that’s = to Stokes particle positive wavelength

Why are Stokes particles going to have more peaks than anti-Stokes, usually just one population more?

Anti-Stokes required pre-charged particles, which is not the dominant state of the molecule. Stokes relies on ground state which is dominant state

What light based technology allowed Raman spectroscopy to be used more extensively?

lasers! without a laser, you don’t have a specific “shot” of photons

What optical element helped allow Raman to become more coherent? This was not a source

double to triple monochromators allowed filtering out stray light to see only Raman photons

What’s the ratio of Raman photons to regular, free flying photons?

1 Raman photon for every 10^8 photons (100 million)

What is special about Raman spectroscopy - or rather, what structural features are best identified by Raman?

protein structure, specifically tertiary and quaternary structure