1. Optical Instrument Components
1.1. Sources of Radiation
1.1.1. Continuum
1.1.1.1. Intensity changes slowly with wavelength
1.1.1.2. UV Region
1.1.1.2.1. Deuterium Lamp
1.1.1.2.2. Hydrogen Lamp
1.1.1.3. Vis Region
1.1.1.3.1. Arc Lamps
1.1.1.3.2. Tungsten Filament Lamp
1.1.1.4. IR
1.1.1.4.1. Heated inert solids
1.1.2. Line
1.1.2.1. Emit a limited number of lines/bands
1.1.2.2. Na and HG vapor lamps
1.1.2.3. Hollow Cathode Lamps (HCL)
1.1.3. Lasers
1.1.3.1. Light Amplification by Stimulated Emission of Radiation
1.1.3.2. High intensities
1.1.3.3. Highly monochromatic
1.1.3.4. Coherent
1.1.3.5. Collimated
1.1.3.5.1. Parallel Rays
1.1.3.6. Polarized
1.1.3.7. Components
1.1.3.7.1. Lasing Medium
1.1.3.7.2. Pumping of lasing medium
1.1.3.7.3. End Cavity mirrors
1.1.3.8. LED
1.1.3.8.1. recombination of electrons and holes in semiconductor produces light
1.1.3.8.2. low cost
1.1.3.8.3. low power consumption
1.2. Wavelength Selectors
1.2.1. Devices used to isolate wavelengths from poly-chromatic sources
1.2.2. Prisms
1.2.2.1. non-parallel faces
1.2.2.2. consequence of refraction
1.2.2.3. Red refracted the least
1.2.2.4. Violet refracted the most
1.2.2.5. Non-linear dispersion
1.2.3. Filters
1.2.3.1. Absorbance
1.2.3.1.1. Restricted to Vis light
1.2.3.2. Interference
1.2.3.2.1. Transparent dielectric
1.2.3.2.2. allows wavelength of interest to pass based on equation
1.2.4. Grating
1.2.4.1. Grooves onto a transparent material
1.2.4.2. light passed through the grating and split into orders
1.2.4.3. Blue diffracted the least
1.2.4.4. Red is diffracted the most
1.2.4.5. Longer wavelength at greater r
1.2.4.6. Give linear dispersion of wavelengths along focal plane
1.2.5. Resolution
1.2.5.1. how well two wavelengths of light can be separated from each other
1.2.5.2. more blazes the better the resolving power
1.3. Sample Container
1.3.1. UV Region
1.3.1.1. Quartz
1.3.1.2. Fused Silica
1.3.2. Vis Region
1.3.2.1. Glass
1.3.2.2. Plastic
1.3.3. IR
1.3.3.1. Salt Plates
1.3.3.2. Diamond
1.3.4. Flame AAS AES
1.3.4.1. No sample container
1.4. Detectors
1.4.1. Thermal
1.4.1.1. IR radiation no photolelectric effect
1.4.1.2. Sense change in temperature
1.4.1.3. slow response times
1.4.1.4. Low Signal to Noise
1.4.2. Photon
1.4.2.1. Respond to incident photon arrival rates
1.4.2.2. Rapid Response times
1.4.2.3. UV/VIs, near-IR radiation
1.4.2.4. Photocathode Tube
1.4.2.4.1. Cathode surface emits electrons when irradiated
1.4.2.4.2. generate photocurrent
1.4.2.4.3. Electrons ejected proportional to radiant Power
1.4.2.5. Photomultiplier Tube (PMT)
1.4.2.5.1. Low Radiant power
1.4.2.5.2. contains many dynodes
1.4.3. Multichannel Devices (MCD)
1.4.3.1. Can measure every wavelength simultaneously
1.4.3.1.1. No scanning
1.4.3.1.2. Quicker analysis
1.4.3.1.3. Less instrumental components
1.4.3.1.4. Can be portable
1.4.3.2. Photodiode Array (PDA)
1.4.3.2.1. 1D
1.4.3.3. Charge Transfer Device
1.4.3.3.1. 2D
2. Fluorescence/Phosphorescence
2.1. Fluorescence
2.1.1. 10^-9
2.1.2. Emission without a change in spin multiplicity, transition always occurs from the lowest singlet excited state
2.1.3. Occurs from the lowest level of an excited electronic state
2.1.4. Absorption takes place before emission
2.1.5. Excitation and emission spectrum are mirror images of each other
2.1.6. pi to pi* transitions
2.1.6.1. Conjugated aromatics
2.1.6.2. Prefers rigidity
2.1.6.3. Fused rings are better
2.1.7. Temperature
2.1.7.1. Cooler is better, decreases number of collisions
2.1.8. Solvents
2.1.8.1. Heavy atoms quench fluorescence
2.1.9. Oxygen
2.1.9.1. promotes intersystem crossing to triplet state
2.1.10. Fluorescence is proportional to incident power
2.2. Phosphorescence
2.2.1. greater than 10^-5
2.2.2. Emission with a change in spin multiplicity. Transition always occurs from the lowest triplet excited state
2.3. Transition from excited singlet to ground singlet is more probable
2.4. Shorter lifetime means greater transition probability
2.5. Quantum Yield
2.5.1. Efficiency of fluorescence under a given set of conditions
2.6. Fluorescence Quenching
2.7. FRET
2.7.1. distance and interactions between proteins with fluorophores
3. IR
3.1. Net change in dipole moment as it vibrates
3.2. Vibrational Modes
3.2.1. Stretching
3.2.1.1. Symmetric
3.2.1.2. Asymmetric
3.2.2. Bending
3.2.2.1. In plane rocking
3.2.2.2. In plane Scissoring
3.2.2.3. Out of plane wagging
3.2.2.4. Out of plane twisting
3.3. Selection Rules
3.3.1. Change dipole moment of the molecule as a result of a molecular vibration
3.3.2. Frequency of the radiation matches the natural frequency of the vibration
3.4. Michelson interferometer
3.4.1. change in path distance= retardation=2* mirror movement
3.4.2. Retardation
3.4.2.1. difference between two paths
3.4.3. Frequency domain signal becomes time domain signal using interferometer
3.4.4. Resolution
3.4.4.1. To resolve to different wavenumbers, the time domain signal must be scanned long enough that one complete cycle for the lines is completed
3.5. Fellgett's Advantage
3.5.1. information at all wavelengths collected simultaneously
3.5.2. improve signal to noise if detector noise dominates
3.6. Connes Advantage
3.6.1. wavelength scale calibrated by laser of known wavelength
3.7. Jacquinot's Advantage
3.7.1. No entrance or exit slit compared to monochromator
3.8. Attenuated Total Reflectance (ATR)
3.8.1. Advantages
3.8.1.1. Minimal sample preparation
3.8.1.2. Excellent for thick of strongly absorbing samples
3.8.1.3. Controlled penetration depth
3.9. Excited to vibrational states
3.10. Asymmetric vibrations active
3.11. IR radiation source
4. The interaction of radiation with matter
4.1. Types of interaction with matter
4.1.1. Absorption
4.1.1.1. An atom or molecule absorbs a photon's energy and is excited from the ground state
4.1.1.1.1. certain matter absorbs certain frequencies
4.1.1.1.2. Radiation must be quantized
4.1.1.1.3. A= - logT
4.1.1.1.4. Transmission
4.1.1.1.5. Beers law
4.1.2. Emission
4.1.2.1. An excited atom or molecule is unstable, returns to the ground state and gets rid of the excess energy by emitting a photon
4.1.3. Scattering
4.1.3.1. Photons bounce off of particles
4.1.4. Reflection
4.1.5. Refraction
4.1.6. Dispersion
4.1.7. Interference
4.1.8. Diffraction
4.1.9. Polarization Rotation
4.2. Relaxation Processes
4.2.1. Nonradiative Decay
4.2.1.1. Energy transfer to other form without emission of light
4.2.1.2. Vibrational Relaxation
4.2.1.2.1. energy transfer to other vibrational modes as kinetic energy
4.2.1.3. Internal Conversion
4.2.1.3.1. allow molecules to pass to a lower energy state without emission of photons
4.2.1.4. Intersystem Crossing
4.2.1.4.1. process of flipping the spin of an excited electron to change multiplicity
4.2.2. Radiative Decay
4.2.2.1. energy transfer to light
5. Properties of Light
5.1. Has both wave and particle like properties
5.2. Slows down when light is traveling through a medium
5.3. Refraction
5.3.1. Snell's Law
5.3.2. Least Time Principle
5.3.3. When going through a different medium light may bend
5.3.4. Critical Angle
5.3.4.1. An angle the provides an angle of refraction of 90 degrees
5.3.4.2. At angles larger than the critical angle no light is refracted
5.4. Reflection
5.4.1. Occurs when light crosses an interface between media of differing refractive index
5.4.2. Incident light intensity may be lost due to reflection
5.4.3. non-Normal Incidence
5.4.3.1. Brewster's Angle
5.4.3.1.1. Angle of incidence at which light with a particular polarization is perfectly transmitted through a transparent surface with no reflection
5.5. Interference
5.5.1. Waves of same frequency experience interference
5.5.2. Constructive
5.5.2.1. Adds together
5.5.3. Destructive
5.5.3.1. Cancel each other out
5.5.3.2. Diffraction pattern
6. Raman Scattering
6.1. Elastic Scattering
6.1.1. Wavelength in = wavelength out
6.2. Inelastic Scattering
6.2.1. shifts in frequency
6.2.2. Related to vibrational changes
6.3. Energy absorbed by molecule from photon not quantized
6.4. Stokes
6.4.1. Shift lower in frequency
6.5. Anti-stokes
6.5.1. Shift higher in frequency
6.6. Change in polarizability
6.6.1. dipole moment induced is proportional to field
6.7. Excited to virtual states
6.8. Symmetric Vibrations active
6.9. Visible radiation source
6.10. Surface enhanced Raman Spectroscopy (SERS)
6.10.1. excitation of localized surface plasmons
6.10.2. single molecule detection
6.10.3. selection rule changes as a result of change in symmetry
6.11. Tip-enhanced Raman Spectroscopy
7. Atomic Spectroscopy
7.1. Line Broadening
7.1.1. Heisenberg Uncertainty Principle
7.1.1.1. linewidth depends on lifetime
7.1.2. Doppler Broadening
7.1.3. Pressure Broadening
7.1.3.1. Due to collisions
7.2. Atomic Absorption Spectroscopy (AAS)
7.2.1. Benefits
7.2.1.1. Easy to use
7.2.1.2. Low maintenance
7.2.1.3. low consumables
7.2.1.4. Measures one element at a time
7.2.2. Sample Introduction
7.2.2.1. Flame Absorption
7.2.2.1.1. Larger droplets hit nebulizer and go to waste
7.2.2.1.2. Sample dissolved into solution
7.2.2.1.3. Advantages
7.2.2.1.4. Disadvantages
7.2.2.2. Electrothermal Vaporization
7.2.2.2.1. Heated graphite furnace
7.2.2.2.2. Advantages
7.2.2.2.3. Disadvantages
7.2.3. Absorbance Source
7.2.3.1. Hollow cathode lamp
7.2.3.1.1. metal of interest
7.2.3.1.2. apply voltage
7.2.3.1.3. ionize gas
7.2.3.1.4. dislodge excited metal atoms which excite radiation
7.2.3.2. Interferences
7.2.3.2.1. Formation of compounds of low volatility
7.2.3.2.2. Ionization
7.2.4. Disadvantages
7.2.4.1. one element at a time
7.2.4.2. Higher chance of chemical interference
7.2.4.3. Tends to be more quantitative
7.3. Atomic Emission Spectroscopy (AES)
7.3.1. Rf induction coil
7.3.2. 3 Concentric Tubes
7.3.3. Spark ionizes and produces seed
7.3.4. Advantages
7.3.4.1. many elements simultaneously
7.3.4.2. lower susceptibility to chemical interference
7.3.4.3. Can be both qualitative and quantitative
7.4. Temperature
7.4.1. Increases atomization efficiency
7.4.2. increase line broadening
7.4.3. decrease peak height
7.4.4. degree of ionization
7.4.5. Use higher temperature for AE
7.4.6. Use lower temperature for AA
8. UV-Vis Absorption
8.1. Promotion of electron from bonding to non-bonding orbital
8.2. Sigma bonds absorb at less than 180nm
8.3. Aromatics (pi transitions) in UV/Vis
8.3.1. Chromophores
8.3.1.1. molecules with unsaturated functional groups
8.3.2. Conjugation
8.3.2.1. lowers energy of pi star yielding absorption max at longer wavelength
8.3.2.2. Bathochromic
8.3.2.2.1. Shift to longer wavelength
8.3.2.3. Hypsochromic
8.3.2.3.1. Shift to shorter wavelength
8.3.2.4. Hyperchromic
8.3.2.4.1. Shift to greater absorbance
8.3.2.5. Hypochromic
8.3.2.5.1. shift to lower absorbance
8.4. Solvents
8.4.1. Want solvents that will not absorb in UV/vis so as not to interfere
8.4.2. Sharp lines are vibrational transition superimposed on electronic transitions
8.5. Instrumentation
8.5.1. Spectrometer
8.5.1.1. photomultiplier
8.5.1.2. reference and sample
8.5.1.3. monochromator
8.5.1.4. Tungsten lamp and Deuterium
8.5.1.5. Light source
8.5.1.5.1. Bright across wide wavelength range
8.5.1.5.2. stable over time
8.5.1.5.3. long service life
8.5.1.5.4. low cost
8.6. Uncertainties
8.6.1. uncertainty has different percent magnitude depending on concentration range