General Raman
Is Raman Qualitative or Quantitative?
Both!
How easily an atom or molecule's electron cloud can be distorted by an external electric field, creating a temporary dipole
Polarizability
What does SERS stand for?
Surface-enhanced Raman scattering
When does scattering occur?
When a monochromatic laser beam interacts with a sample.
What must molecules possess for resonance raman?
Chromophore
Raman is usually used complimentary to what technique?
IR
Regions on a metal surface where the electromagnetic field is highly intensified
Hot Spots
Most widely used substrates in SERS due to their plasmonic properties
Silver and Gold
This scattered radiation has the same radiation as the source radiation and occurs as a result of elastic collisions between the photons and the molecules in the sample
Rayleigh Scattering
Is a normal Raman spectra or a resonance spectra simpler?
Resonance
Why is Raman good for wet samples and aqueous solutions in comparison to IR?
Water is a weak Raman scatterer but a strong absorber of IR radiation
The name of a technique that increases the intensity of Raman by 103 - 106
Resonance Raman
Name 3 applications for SERS
disease biomarkers, drug development, corrosion, catalysis, explosive detection, food safety, environmental analysis, forensic science, and archaeology
Occurs when the scattered photon loses energy to the molecule, resulting in a lower frequency and longer wavelength.
Stokes scattering
What can resonance Raman be used to study?
Very low concentrations of biologically important molecules
How does Raman complement IR absorption spectroscopy? Name 3 Reasons
Some vibrations are not absorbed in the IR region
Vibrations are only seen if there is a change in the dipole moment during it
A change in polarizability is necessary
Some vibrations are active in IR and not in Raman
In general, symmetric vibrations give rise to intense Raman lines; nonsymmetric ones are usually weak and sometimes unobserved.
Monochromatic light from a laser that illuminates a sample to initiate the Raman scattering process
Incident Light
The amplification of Raman signals can be enhanced by what two different mechanisms?
Electromagnetic enhancement and charge transfer.
Happens when the scattered photon gains energy from a molecule that is already in an excited vibrational state, leading to a higher frequency and shorter wavelength
Anti-stokes scattering
What wavelengths are used for resonance Raman?
UV and visible
Name 3 major advantages for using Raman
Few concerns with sample thickness
Little interference from ambient atmosphere
Vacuums and purge gases not necessary
Glass, water, and plastic packaging have weak spectra, so they can be measured directly inside their package (minimizing contamination)
Aqueous samples are readily analyzed
No 2 compounds have the same Raman spectra
The intensity of the scattered light is proportional to the amount of material present
Raman is qualitative and quantitative!
When electrons are disturbed from equilibrium they produce a quantum of plasma oscillation or a "sea of electrons"
Plasmons
Name the 5 metals used as surfaces in SERS
Gold, silver, copper, platinum, and palladium
What type of light interferes with stokes lines and why?
Fluorescent light is much stronger than Raman, and can produce an intense background that overlaps with the stokes region and drowns it out
This type of laser uses an organic dye solution to change its output wavelength
Tunable dye laser