Lecture 3 - Spectroscopic Techniques Flashcards
What type of spectroscopy is raman?
vibrational spectroscopy
what is raman based on?
photons interacting with the molecular vibrations in materials and are scattered
what are the two types of photon scattering?
elastic and inelastic scattering
what is elastic scattering?
when the photon leaves the molecule in the same quantum state = Rayleigh scattering
what is inelastic scattering?
when the photon leaves the molecule in a different quantum state = Raman scattering
what are the two types of raman scattering?
stokes and anti stokes
what is meant by stokes and anti-stokes?
stokes = the photon loses energy to the molecule
anti-stokes = the photon gains energy from the molecule
what do scattered photons emit?
certain wavelenghts of light which correspond to their energy
in raman spectroscopy how is the majority of light scattered?
elastically (Rayleigh), for every 1 in 10 million photons we get raman scattering
if a photon loses energy to the molecule what has happened to the energy of the molecule?
the molecule’s energy increases
raman scattering does not consider electronic transitions so what does it consider?
virtual states
name 6 types of molecular vibrations
symmetric stretch
asymmetric stretch
in plane scissoring
in plane rocking
out of plane wagging
out of plane twisting
to be raman active what must a molecule have?
anisotropic polarizability (refers to the ability of a molecule to be polarised by an external electric field)
if something changes polarisability what does this mean?
the shape of the electron cloud around the molecule shifts
what needs to change for a molecule to be IR active?
the dipole moment
what corresponds to a change in polarisability?
the stretching of a molecule