1. Radiation
1.1. Sources of Radiation
1.1.1. Continuum: intensity changes slowly with wavelength
1.1.1.1. UV Region
1.1.1.1.1. Deuterium
1.1.1.1.2. Hydrogen
1.1.1.2. Intense
1.1.1.2.1. Arc lamps of Ar, Xe, or Hg
1.1.1.3. Vis Region
1.1.1.3.1. W filament lamp
1.1.1.4. Infrared
1.1.1.4.1. Heated inert solids
1.1.2. Line Sources: emit a limited number of lines/bands
1.1.2.1. Na and Hg vapor lamps
1.1.2.2. Hollow cathode lamps
1.1.3. Lasers: Light Amplification by Stimulated Emission of Radiation
1.1.3.1. Properties
1.1.3.1.1. High intensity
1.1.3.1.2. High power
1.1.3.1.3. Highly monochromatic
1.1.3.1.4. Coherent
1.1.3.1.5. Collimated
1.1.3.1.6. Polarized
1.1.3.2. Components
1.1.3.2.1. Lasing medium
1.1.3.2.2. Pumping of lasing medium
1.1.3.2.3. End cavity mirrors
1.1.3.3. Laser Diode
1.1.3.3.1. Population inversion of charge carriers in a semiconductor is achieved by a high electric field across a pn junction
1.2. Wavelength Selectors: Devices used to isolate wavelengths from polychromatic sources
1.2.1. Filters
1.2.1.1. Absorbance Filter
1.2.1.1.1. Restricted to visible light
1.2.1.1.2. Typically colored glass
1.2.1.1.3. Absorb unwanted light
1.2.1.2. Interference Filter (Fabry Perot Filter)
1.2.1.2.1. Transparent dielectric between two metal films
1.2.1.2.2. Allows wavelength of interest to pass
1.2.1.2.3. λ = (2dη)/m
1.2.2. Prisms
1.2.2.1. Contains non-parallel faces
1.2.2.2. Light is dispersed at the interfaces
1.2.2.2.1. Red refracted the least
1.2.2.2.2. Violet refracted the most
1.2.3. Gratings
1.2.3.1. Transmission Diffraction Grating
1.2.3.1.1. Grooves ruled onto a transparent material
1.2.3.1.2. Beam of light passed through is partly split into orders with spectra on either side of it
1.2.3.1.3. Blue light diffracted the least; Red light diffracted the most
1.2.3.2. nλ = d[sin(i) + sin(r)]
1.3. Radiation Detectors
1.3.1. Thermal Detector
1.3.1.1. IR radiation can't produce photoelectric effect
1.3.1.2. Senses change in temperature associated with absorbing radiation
1.3.1.3. Slow response times
1.3.1.3.1. Low S/N
1.3.1.4. Used for IR
1.3.2. Photon Detector
1.3.2.1. Responds to incident photon arrival rates
1.3.2.2. Rapid response time
1.3.2.3. Used for UV, Vis, and near-IR radiation
1.3.2.4. Types
1.3.2.4.1. Photocathode Tube
1.3.2.4.2. Photomultiplier Tube (PMT)
1.3.2.4.3. Vacuum Phototubes
1.3.3. Multichannel Devices (MCD)
1.3.3.1. Can measure every wavelength simultaneously
1.3.3.1.1. No scanning
1.3.3.1.2. Quicker analysis
1.3.3.1.3. Less instrumental components
1.3.3.1.4. Instrument can be portable
1.3.3.2. Photodiode Array (PDA)
1.3.3.2.1. 1-Dimensional
1.3.3.3. Charge Transfer Device (CTD)
1.3.3.3.1. 2-Dimensional
1.3.3.3.2. Charge Injection Device (CID)
1.3.3.3.3. Charge Coupled Device (CCD)
2. Spectroscopic Methods
2.1. Atomic Absorption
2.1.1. Advantages & Disadvantages
2.1.1.1. Comparatively easy to use
2.1.1.2. Low maintenance
2.1.1.3. Low consumables
2.1.1.4. Good for measuring one element at a time
2.1.1.5. Sample dissolved into solution
2.1.1.5.1. Larger droplets from the nebulizer hit the spoiler and go to waste
2.1.1.6. Precision: 1% or better
2.1.1.7. Residence time for particles is short
2.1.1.7.1. Vaporization efficiency is poor
2.2. Electrothermal Vaporization
2.2.1. Advantages & Disadvantages
2.2.1.1. Small amount of sample required
2.2.1.2. Excellent LOD
2.2.1.3. More sensitive than flame
2.2.1.4. Entire sample atomized at once
2.2.1.5. Residence time in optical path >1 second
2.2.1.6. Poor precision due to sampling variability
2.2.1.7. Narrow analytical range
2.3. Atomic Emission
2.3.1. Advantages & Disadvantages
2.3.1.1. Can simultaneously analyze many elements with a sample
2.3.1.2. Lower susceptibility to chemical interference
2.3.1.3. Both qualitative and quantitative
2.3.2. Boltzmann Distribution
2.3.2.1. Used to calculated the proportion of excited state atoms
2.3.3. Effects of Temperature Increase
2.3.3.1. Increased atomization efficiency
2.3.3.2. Increased line broadening
2.3.3.3. Decreased peak height
2.3.3.4. Degree of ionization
2.4. Atomic Fluorescence
2.4.1. Deactivation Processes
2.4.1.1. Radiative: emission of a photon
2.4.1.2. Non-Radiative
2.4.1.2.1. Internal Conversion
2.4.1.2.2. Vibrational Relaxation
2.4.2. Structure
2.4.2.1. Molecules with low energy pi-pi* transitions
2.4.2.1.1. Conjugated aromatics
2.4.2.2. Rigid rings
2.4.2.2.1. Simple heterocycles do not fluoresce
2.4.2.2.2. Single ring compounds have weak fluorescence
2.4.2.2.3. Fused rings fluoresce more strongly
2.4.2.2.4. Conjugated systems fluoresce strongly
2.4.3. Conditions
2.4.3.1. Temperature
2.4.3.1.1. Cooler temperature lead to higher quantum yields and an increase in viscosity of the solvent
2.4.3.2. Solvent
2.4.3.2.1. Solvents with heavier atoms will quench fluorescence and increase phosphorescence
2.4.3.3. Oxygen
2.4.3.3.1. Promotes intersystem crossing and usually quenches fluorescence
2.4.3.4. Fluorescence Quenching
2.4.3.4.1. Stern-Volmer Relationship
2.5. Raman Spectroscopy
2.5.1. Measures changes in polarizability
2.5.2. Complementary to Infrared Spectroscopy
2.5.2.1. Frequency shifts are related to vibrational changes in the molecule
2.5.2.2. Raman scattering spectrum resembles IR absorbance spectrum
2.5.3. Rayleigh Scattering
2.5.3.1. E_before = E_after
2.5.3.2. λ_in = λ_out
2.5.4. Surface Enhanced Raman Spectroscopy (SERS)
2.5.4.1. Excitation of localized surface plasmons
2.5.4.2. Single molecule detection
2.5.4.3. Selection rule changes as a result of change in symmetry
2.5.5. Tip-Enhanced Raman Spectroscopy (TERS)
2.5.5.1. Can be coupled with other scanning probe techniques
2.5.5.1.1. Scanning Electrochemical Microscope (SECM)
2.5.5.1.2. Atomic Force Microscope (AFM)
2.5.5.1.3. Scanning Tunneling Microscope (STM)
3. What is Spectroscopy?
3.1. Interaction of radiation with matter
3.1.1. Electromagnetic Radiation
3.1.1.1. Light
3.1.1.2. Heat
3.1.1.3. Gamma Rays
3.1.1.4. X-Rays
3.1.1.5. UV–Vis
3.1.1.6. Microwave
3.1.1.7. RF
3.1.2. Non-Electromagnetic Radiation
3.1.2.1. Acoustic Waves
3.1.2.2. Beams of Particles
4. Light
4.1. Fundamental Processes
4.1.1. Absorption
4.1.2. Emission
4.1.3. Scattering
4.1.4. Reflection
4.1.4.1. Occurs when hv crosses an interface between media of differing refractive index
4.1.4.1.1. [(I_r)/(I_i)] = [(n_2 – n_1)^2]/[(n_2 + n_1)^2]
4.1.5. Refraction
4.1.5.1. Snell's Law
4.1.5.1.1. [sin(theta_1)/sin(theta_2)] = (n_2)/(n_1) = (v_1)/(v_2)
4.1.6. Dispersion
4.1.7. Interference
4.1.8. Diffraction
4.1.9. Polarization Rotation
4.1.9.1. Unpolarized
4.1.9.2. Plane Polarized
4.2. Wave or Particle?
4.2.1. Wave
4.2.1.1. Wavelength, frequency, wave number
4.2.1.1.1. c = λv
4.2.1.1.2. v ̅ = 1/λ
4.2.1.2. Behavior of Light Waves
4.2.1.2.1. Interference: waves of same frequency experience interference
4.2.1.2.2. Constructive: waves adds together
4.2.1.2.3. Destructive: waves cancel each other out
4.2.2. Particle
4.2.2.1. Energy of light is quantized
4.2.2.1.1. E = hv = hc/λ = hcv ̅
4.3. Traveling Light Waves
4.3.1. Transmission: light traveling through a medium
4.3.1.1. c = nv
4.3.1.1.1. n: refractive index
4.3.1.1.2. v: velocity of light
4.3.1.2. η > 1
4.3.1.2.1. Light travels slower through media
4.4. Thin Lenses
4.4.1. 1/f = 1/s + 1/s'
4.4.1.1. f: focal length
4.4.1.2. s: objective distance
4.4.1.3. s': image distance
4.4.2. M = s'/s
4.5. Curved Reflective Surfaces
4.5.1. Mirrors are achromatic
4.5.2. f = –R/2
5. Interactions of Light with Matter
5.1. Absorption
5.1.1. An atom or molecule absorbs a photon energy and is excited from the ground state
5.1.1.1. Certain frequencies of radiation may be selectively absorbed by matter
5.1.1.2. Energy from the radiation is transferred to the matter
5.1.1.3. Radiation must be "quantized" to the energy level in the matter to be absorbed
5.1.2. Absorbance & Transmittance
5.1.2.1. Transmittance: the ratio of the source radiation power to the incident power
5.1.2.1.1. T = P_T/P_0
5.1.2.2. Absorbance: another way to measure the attenuation of hv
5.1.2.2.1. A = –log(T)
5.1.3. Beer's Law
5.1.3.1. A = ϵbC
5.1.3.1.1. ϵ: molar absorptivity
5.1.3.1.2. b: pathlength
5.1.3.1.3. C: concentration
5.1.3.2. Deviations from Beer's Law
5.1.3.2.1. High concentrations
5.1.3.2.2. Neighbor effect
5.1.3.2.3. Polychromatic radiation
5.1.3.2.4. Changes in effective molar absorptivity of species
5.2. Emission & Luminescence
5.2.1. An excited atom or molecule is unstable, returns to the ground state, and gets rid of the excess energy by emitting a photon
5.2.1.1. Sources of Excitation
5.2.1.1.1. Electrons
5.2.1.1.2. X-Rays
5.2.1.1.3. Heat
5.2.1.1.4. Current
5.2.1.1.5. Irradiation
5.2.1.1.6. Chemical Reaction
5.2.1.2. Types of Spectrum
5.2.1.2.1. Line: excitation of individual atoms
5.2.1.2.2. Band: from small molecules or radicals
5.2.1.2.3. Continuum: blackbody radiation
5.2.1.3. Relaxation Processes
5.2.1.3.1. Non-radiative Decay
5.2.1.3.2. Radiative Decay
5.2.1.3.3. Vibrational Relaxation
5.2.1.3.4. Internal Conversion
5.2.1.3.5. Intersystem Crossing
5.3. Scattering
5.3.1. Photons bounce off of particles