 Lecture 30 11/14/05. Spectrophotometry Properties of Light h = 6.626 x 10 -34 J-s c = 3.00 x 10 8 m/s.

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Lecture 30 11/14/05

Spectrophotometry

Properties of Light h = 6.626 x 10 -34 J-s c = 3.00 x 10 8 m/s

 Transmittance  Absorbance P = Irradiance (Intensity) = energy per second per area of light

Beer’s Law A=  bc  = extinction coefficient or molar absorptivity b = pathlength c = concentration

Recap  Absorbance Specific wavelengths of light electronic transition UV/Vis: electronic transition Vibrations IR: Vibrations  Beer’s Law For Quantitation

Beer’s Law  Monochromatic light  Dilute solutions

IC: Internal conversion ISC: Intersystem crossing

Luminescence  Fluorescence Emission of photon during transition between S 1  S 0  Phosphorescence Emission of photon during transition between T 1  S 0

Luminescence  More sensitive than absorption  Lower energy (higher wavelength) than the energy absorbed

IC: Internal conversion ISC: Intersystem crossing

I = kP 0 c

 Excitation spectrum vs. emission spectrum

Analysis of a Mixture  A =  X b[X] +  Y b[Y] +  Z b[Z] +....

Spectra overlap 1.Constant concentration of both analytes 1. Find  at different 2.Least squares to find best values of [X] and [Y] 1. A m =  X b[X] +  Y b[Y] 2. A calc =  X b[X] guess +  Y b[Y] guess

Spectra not-overlapping A’ =  ’ X b[X] +  ’ Y b[Y] at ’ A’’ =  ’’ X b[X] +  ’’ Y b[Y] at ’’

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Recap  Absorbance Specific wavelengths of light electronic transition UV/Vis: electronic transition Vibrations IR: Vibrations  Beer’s Law For Quantitation

Beer’s Law  Monochromatic light  Dilute solutions

IC: Internal conversion ISC: Intersystem crossing

Luminescence  Fluorescence Emission of photon during transition between S 1  S 0  Phosphorescence Emission of photon during transition between T 1  S 0

Luminescence  More sensitive than absorption  Lower energy (higher wavelength) than the energy absorbed

IC: Internal conversion ISC: Intersystem crossing

I = kP 0 c

 Excitation spectrum vs. emission spectrum

Analysis of a Mixture  A =  X b[X] +  Y b[Y] +  Z b[Z] +....

Spectra overlap 1.Constant concentration of both analytes 1. Find  at different 2.Least squares to find best values of [X] and [Y] 1. A m =  X b[X] +  Y b[Y] 2. A calc =  X b[X] guess +  Y b[Y] guess

Spectra not-overlapping A’ =  ’ X b[X] +  ’ Y b[Y] at ’ A’’ =  ’’ X b[X] +  ’’ Y b[Y] at ’’

`

Recap  Absorbance Specific wavelengths of light electronic transition UV/Vis: electronic transition Vibrations IR: Vibrations  Beer’s Law For Quantitation

Beer’s Law  Monochromatic light  Dilute solutions

IC: Internal conversion ISC: Intersystem crossing

Luminescence  Fluorescence Emission of photon during transition between S 1  S 0  Phosphorescence Emission of photon during transition between T 1  S 0

Luminescence  More sensitive than absorption  Lower energy (higher wavelength) than the energy absorbed

IC: Internal conversion ISC: Intersystem crossing

I = kP 0 c

 Excitation spectrum vs. emission spectrum

Analysis of a Mixture  A =  X b[X] +  Y b[Y] +  Z b[Z] +....

Spectra overlap 1.Constant concentration of both analytes 1. Find  at different 2.Least squares to find best values of [X] and [Y] 1. A m =  X b[X] +  Y b[Y] 2. A calc =  X b[X] guess +  Y b[Y] guess

Spectra not-overlapping A’ =  ’ X b[X] +  ’ Y b[Y] at ’ A’’ =  ’’ X b[X] +  ’’ Y b[Y] at ’’

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