spectroscopy

• What is the lambert beer law?


  I = I0 * 10^(-EBC)
• What is the formula for absorbance?


  A = -logT = log (I0 / I)
• what is absorption?


  Light (radiation) is absorbed by the matter
• What is scattering?


  reflection of light via radiation : antistokes , rayleigh and stokes.

  
  

  Anti stokes: occurs when energy is higher than initial energy

  
  

  Rayleigh: occurs when energy equals initial energy

  
  

  Stokes: Occurs when energy is less than initial
• What are the characteristics of electromagnetic radiation?


  Period: T

  Frequency: 1/T

  Wavelength: C/V

  Wavenumber: 1/ lambda
• What is the formula for the energy of a particle of light (photon) ?


  E = h * v

  
  

  h = placks constant

  V = frequency
• What are the characteristics of the electromagnetic spectrum?


  Radio: Low wave length , low energy

  
  

  Microwave: higher energy ,, rotational spectroscopy
• What is the molecular motion of particles?

  Bending , stretching
• How to calculate transmittance?

  T = I (output) / I0 (input)
• What is the Beer-Lambert Law?


  A = Ebc

  
  

  E =absorptivity

  B = path length

  C = concentration
• What is the Franck-Condon principle?


  electronic transitions occur much more quickly than the change in nuclei distances, so only the overlap between initial and final vibrational wavefunctions matters for the probability a transition will occur
• What factors affect energy and nuclear distance?


  Temperature: affects peaks (absorption) , high temp wide peak , low temp narrow

  
  

  Structure: increase degree of condensation (electrons have lower energy)

  
  

  solvent polarity: increased polarity decreases energy change so needs photon of lower energy to excite it
• What is the bathochromic shift?

  position of a peak shift to a lower energy , longer wavelength
• What is a hypochromic shift?

  Increasing polarity will increase energy change , shift to shorter wavelength , higher energy
• What is the isosbestic point?

  a wavelength at which the absorption of light by mixed solution remains constant as there is an equilibrium
• What is a Jablonski diagram?


  represents all pathways of excitation
• What is the radiative process?

  Return to ground state with release of energy through light
• What is the internal conversion in a jablonski diagram?


  non radiative emission when electron moves from higher level of energy to a lower level when vibrations of different electronic levels overlap.
• What is vibration relaxation?


  non-radiative loss of energy between vibrational energy levels. This excess vibrational energy is lost as kinetic energy to other vibrational modes, either of the same molecule or of a different molecule
• What is phosphorescence?


  type of fluorescence in which an electron relaxes into the ground state via emission of a photon. However, unlike in fluorescence, the electron must change spin states for this to occur. This is a forbidden transition, so happens over a much longer time scale
• What is intersystem crossing?


  non-radiative emission the spin state of the excited electron changes
• What is the stokes shift?


  the difference between the peak absorbance and peak emission wavelengths of a fluorochrome
• What is the formula for fluorescence quantum yield?

  Emitted intensity / absorbed intensity
• What is the fluorescence lifetime equation?


  T0 = 1/kf + Kisc + Kic
• How does condensation and rigidity affect fluorescence?


  Condensation: higher degree increases fluorescence as they can absorb more light

  
  

  rigidity: The more rigid, the more fluorescence as there is a higher quantum yield
• How do hetero atoms and heavy atoms affect fluorescence?


  Decrease fluorescence because there is a lower quantum yield
• How does temperature , viscosity and ph affect fluorescence?


  Temperature: increase temperature decreases fluorescence as there is more collisions and therefore higher chance of external conversion

  
  

  Viscosity: Increase viscosity increases fluorescence as there are less collisions and so less chance of deactivation

  
  

  PH: increasing ph increases fluorescence as NH2 and OH are electron donors therefore releasing energy
• How does dissolved oxygen and concentration affect fluorescence?


  O2: Increased oxygen concentration decrease fluorescence as it allows for less light to be emitted therefore no fluorescence

  
  

  Conc: If we decrease concentration of compound then less fluorescence
• What is fluorescence quenching?


  Any process that decreases fluorescence intensity
• What are examples of fluorescence quenching?


  Collisional deactivation , electron transfer and fluorescence resonance energy transfer (FRET)
• What is the formula for collisional deactivation? (stern volmer eq)?


  I0/I = Φ0/Φ = 1 + T0 *Kq (Q)
• What is the fret efficiency formula?


  N = 1- Φ/Φ0 = 1- I/I0
• What is the forster distance (Ro)


  Separation corresponding to 50% of maxiumum RET efficiency