Chapter 6 Flashcards
Spectophotometry
measures chemical concentration using light(electromagnetic radiation)
Four frequency decoding devices
prisms, diffraction gratings, Michelson interferometer, Fabry-Perot interferometer
Diffraction gratings
uses diffraction and interference to separate light into different wavelengths. more lines/mm = greater separation
Prisms
separate light into its wavelengths due to a difference in refractive index
Coherent radiation
Diffraction of electromagnetic energy through two slits, must be coherent such that waves of the same frequency and phase relationship to create the band pattern imaged below
Super position Principal
constructive and destructive interference of electromagnetic waves that occupy the same domain
Refractive index of a medium
Determines how much EMR will bend when it passes from a substance of one density to a substance f another
Dispersion
When refractive endex changes with changes in wavelength or frequency
Normal dispersion of a substance
Gradual change in refractive index as the frequency changes
Anomalous dispersion
As frequency changes, there is a sharp change in refractive index. This is the frequency at which the analyte will absorb
Work function of a substance
A CONSTANT SPECIFIC TO EACH METAL MATERIAL COATING A PHOTOTUBE THAT SPECIFIES THE MINIMUM ENERGY OF THE BINDING ELECTRON
Photoelectric effect
EMR acts as both a particle(photon) and a wave
ground state of a molecule
All electrons in predicted energy levels. Lowest energy state.
electronic excitation
moving an electron from its ground state to a higher energy
fluorescence
Photon in photon out. Light that is re-emitted will be the same (resonance fluorescence=atoms), or lower in energy (non-resonance fluorescence).
Phosphorescence
When an excited molecule relaxes into a triplet state. Much longer lifespan than fluorescence.
Transmittance
The portion EMR that is not absorbed, because not at the correct wavelength to meet the harmonics of the molecule.
Absorptivity
The ability of a molecule to absorb light at a particular wavelength
Absorbance
The amount of light absorbed by a sample.
Vibrational relaxation
A electron moves from a higher vibrational state back to its ground state. This happens before electronic relaxation.
Stokes and anti-stokes
In the contextof Raman scattering: a photon hits a particle, and is scattered.
Stokes: the photon that is scattered has a lower energy
Anti-stokes: the photon scattered has higher energy
Coherent Radiation
Phases of two or more waves representing the radiation differ by a known constant. Ex: laser radiation
Superposition principal
waves of radiation can overlap. Think constructive/destructive interference
Refractive index
The speed light travels through a medium compared to the speed of light in a vacuum.
n=c/v
n=refractive index
c=speed of light in a vacuum
v=velocity of radiation in the medium
Normal dispersion
ratio of refractive index (n) to the wavelength of light (lambda)
Anomalous dispersion
Incident radiation matches the natural harmonics of a molecule. Therefore absorbance occurs.
work function
minimum energy needed to remove an electron t=from the surface of a substance.
Photoelectric effect
photon in. Electron out.
Ground state
lowest energy level
electronic excitation
Electron excited to a higher energy state
Fluorescence
- excited.
- loss of vibrational energy. (non-radiative decay meaning no light lost)
- emits lights back to ground state.
phosphorescence
- excited
- decay with a spin flip(therefore takes much longer than fluorescence)
- light emitted. back to ground state
stokes shift
emitting photon is less than the absorbed photon.
