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Daniel C. Harris Quantitative Chemical Analysis Seventh Edition Chapter 18 Fundamentals of Spectrophotometry Copyright Daniel C. Harris Quantitative Chemical Analysis Seventh Edition Chapter 18 Fundamentals of Spectrophotometry Copyright © 2007 by W. H. Freeman and Company

Light has: • Intensity • Color (wavelength) • Polarization Light has: • Intensity • Color (wavelength) • Polarization

• Intensity • Intensity

Transmittance Absorbance Transmittance Absorbance

Transmittance Absorbance Beer’s Law Transmittance Absorbance Beer’s Law

ε = 313 M-1 cm-1 b = 2 cm T = 3. 16% = ε = 313 M-1 cm-1 b = 2 cm T = 3. 16% = 0. 0316 A = -log. T = 1. 50 c = 1. 5/(313 M-1) (2 cm-1) = 0. 0024 M

d. P(x)/dx = -κ P(x) = exp(-κ x) d. P(x)/dx = -κ P(x) = exp(-κ x)

Beer’s law Beer’s law

Molar extinction Coefficient ~250 L. mol-1 cm-1 Cross section ~10 -18 cm 2 Molar extinction Coefficient ~250 L. mol-1 cm-1 Cross section ~10 -18 cm 2

Absorption of a mixture Absorption of a mixture

Isosbestic point Isosbestic point

(wavelength) x (frequency) = speed [m/s] λν = c [108 m/s] (wavelength) x (frequency) = speed [m/s] λν = c [108 m/s]

436 nm what frequency? 436 nm what frequency?

Visible spectrum Visible spectrum

Your Eyes See the Color that is NOT Absobed Your Eyes See the Color that is NOT Absobed

Hexaquotitanium (III) Solutions Appear Violet Due to Absorption of Yellow and Green Light Hexaquotitanium (III) Solutions Appear Violet Due to Absorption of Yellow and Green Light

Subtraction of Light by Absorption Leads to Color you See Subtraction of Light by Absorption Leads to Color you See

What makes a molecule absorb light? What makes a molecule absorb light?

What makes a molecule absorb light? What makes a molecule absorb light?

What makes a molecule absorb light? Electron motion (fs) resonant frequency ~ 10 -15 What makes a molecule absorb light? Electron motion (fs) resonant frequency ~ 10 -15 s ν ≈ 1015 s-1 ~ 300 nm UV-VIS

What makes a molecule absorb light? Electron motion UV-VIS excites electrons! What makes a molecule absorb light? Electron motion UV-VIS excites electrons!

E=hν E=hν

E=hν E=hν

E=hν E=hν

E=hν E=hν

Electron diffraction pattern from a beryllium atom Electron diffraction pattern from a beryllium atom

What makes a molecule absorb light? Nuclear motion ~ 3000 nm infrared What makes a molecule absorb light? Nuclear motion ~ 3000 nm infrared

What makes a molecule absorb light? Nuclear motion ~ 300, 000 nm microwave What makes a molecule absorb light? Nuclear motion ~ 300, 000 nm microwave

What makes a molecule absorb light? Oscillating DIPOLE moment What makes a molecule absorb light? Oscillating DIPOLE moment

What makes a molecule absorb light? What makes a molecule absorb light?

What makes a molecule absorb light? What makes a molecule absorb light?

What makes a molecule absorb light? green house gas http: //science. widener. edu/svb/ftir/ir_co 2. What makes a molecule absorb light? green house gas http: //science. widener. edu/svb/ftir/ir_co 2. html

What makes a molecule absorb light? [cm-1] = 1/λ = ν/c =E/hc What makes a molecule absorb light? [cm-1] = 1/λ = ν/c =E/hc

What makes a molecule absorb light? 3200 cm− 1 broad, strong O-H stretch (alcohols) What makes a molecule absorb light? 3200 cm− 1 broad, strong O-H stretch (alcohols) 3000 cm− 1 broad, medium O-H stretch (carboxylic acids) 1200 cm− 1 strong, O-H bending 2800 cm− 1 strong, C-H stretch 1400 cm− 1 variable, C-H bending 1700 cm− 1 strong, C=O stretch 1200 cm− 1 strong, C-O stretch

What makes a molecule absorb light? What makes a molecule absorb light?

What makes a molecule absorb light? What makes a molecule absorb light?

E=hν E=hν

E=hν E=hν