The learning objectives for this course are: (1) Critically consume scientific literature and talks...

The learning objectives for this course are:The learning objectives for this course are:

(1)(1) Critically consume scientific literature and talks in the area Critically consume scientific literature and talks in the area of analytical spectroscopy. Pose meaningful questions and of analytical spectroscopy. Pose meaningful questions and present significant comments while exploring a new topic.present significant comments while exploring a new topic.

(2) Identify appropriate spectroscopic techniques for the (2) Identify appropriate spectroscopic techniques for the analysis of any sample. Recognize the strengths and analysis of any sample. Recognize the strengths and limitations of each technique.limitations of each technique.

(3) Formulate a novel research project addressing an (3) Formulate a novel research project addressing an important unanswered question by exploiting analytical important unanswered question by exploiting analytical spectroscopic methods. Recognize the critical early work spectroscopic methods. Recognize the critical early work and identify current state-of-the-art work in the chosen area.and identify current state-of-the-art work in the chosen area.

A few “housekeeping” issues:A few “housekeeping” issues:

(1)(1) Questions about syllabus?Questions about syllabus?

(2) Trouble with the blog?(2) Trouble with the blog?

(3) Sign up for ASAP alerts(3) Sign up for ASAP alerts

Why is Why is Analytical SpectroscopyAnalytical Spectroscopy Important? Important?

Spectroscopy EM Radiation SourcesSpectroscopy EM Radiation Sources

No radiation:No radiation: Excitation by collisions or chemical reactions can Excitation by collisions or chemical reactions can initiate photon emission. initiate photon emission.

Continuum Source:Continuum Source: Emit radiation over a broad wavelength Emit radiation over a broad wavelength range (e.g. incandescent lamps)range (e.g. incandescent lamps)

Line Source:Line Source: Emit radiation at discrete wavelengths (e.g. Hg Emit radiation at discrete wavelengths (e.g. Hg arc lamp, laser).arc lamp, laser).

Image source: www.oceanoptics.comImage source: www.oceanoptics.com

Tungsten Halogen LampTungsten Halogen Lamp Mercury Argon LampMercury Argon Lamp

Interaction between EM Radiation and the Interaction between EM Radiation and the SampleSample

absorbabsorbradiationradiation

radiationlessradiationlessabsorptionabsorption

emitemitradiationradiation

radiationlessradiationlessemissionemission

emissionemission absorptionabsorption photoluminescencephotoluminescence

inelastic excitation or deactivationinelastic excitation or deactivation

Atomic vs. Molecular SpectroscopyAtomic vs. Molecular Spectroscopy

Atomic Spectroscopy Example (ClAtomic Spectroscopy Example (Cl22):):

Molecular Spectroscopy (CHMolecular Spectroscopy (CH33CHCH22OH):OH):

Image source: www.wikipedia.orgImage source: www.wikipedia.org

Wavelength Selection before DetectionWavelength Selection before DetectionMust separate analyte optical signal from a majority of the Must separate analyte optical signal from a majority of the potentially interfering optical signals.potentially interfering optical signals.

- absorption filters- absorption filters - interference filters- interference filters - spatial dispersion- spatial dispersion - interferometry- interferometry

Image source: www.wikipedia.orgImage source: www.wikipedia.org

Are you getting the concept?Are you getting the concept?

The two transmission profiles below are for filters sold The two transmission profiles below are for filters sold by Melles-Griot. Which filter would you buy to block by Melles-Griot. Which filter would you buy to block = 15,800 cm= 15,800 cm-1-1 light? light?

(a)(a) (b)(b)

Radiant Power Monitors (a.k.a. Detectors)Radiant Power Monitors (a.k.a. Detectors)Detectors convert EM radiation Detectors convert EM radiation into an electrical signal or into an electrical signal or another physical quantity that can another physical quantity that can easily be converted into an easily be converted into an electrical signal.electrical signal.

Thermal Detectors:Thermal Detectors: convert IR convert IR radiation into current or voltageradiation into current or voltagePhoton Detectors:Photon Detectors: convert UV convert UV and visible photons into currentand visible photons into currentMultichannel Detectors:Multichannel Detectors: convert convert UV and visible photons into UV and visible photons into chargecharge

Skoog and Leary, Principles of Instrumental Analysis, Skoog and Leary, Principles of Instrumental Analysis, Saunders College Publishing, Fort Worth, 1992.Saunders College Publishing, Fort Worth, 1992.

Review:

Are you getting the concept?

Are you getting the concept?Are you getting the concept?

Calculate the energy of (a) a 5.30 Calculate the energy of (a) a 5.30 ÅÅ X-ray photon (in X-ray photon (in eVs) and (b) a 530-nm photon of visible radiation (in eVs) and (b) a 530-nm photon of visible radiation (in kJ/mole).kJ/mole).

Are you getting the concept?Are you getting the concept?Sketch the sum wavefunction of the red and blue waves.Sketch the sum wavefunction of the red and blue waves.

0.5

-0.5

1.0

-1.0

kx

0.5

-0.5

1.0

-1.0

kx

Are you getting the concept?Are you getting the concept?If the average irradiance from the Sun impinging normally on a If the average irradiance from the Sun impinging normally on a surface just outside the Earth’s atmosphere is 1400 W/msurface just outside the Earth’s atmosphere is 1400 W/m22, what is , what is the resulting pressure (assuming complete absorption)? How the resulting pressure (assuming complete absorption)? How does this pressure compare with atmospheric pressure (~ 10does this pressure compare with atmospheric pressure (~ 1055 N/mN/m22)?)?

Reminder: 1 W = 1 J/s = 1 NReminder: 1 W = 1 J/s = 1 N··m/s = 1 kgm/s = 1 kg··mm22/s/s33

Are you getting the concept?Are you getting the concept?Many streetlights are sodium discharge lamps. The emitted Many streetlights are sodium discharge lamps. The emitted orange light is due to the sodium D-line transition: orange light is due to the sodium D-line transition:

What is the energy level spacing (in eV) for What is the energy level spacing (in eV) for the 3p the 3p → 3s transition?→ 3s transition?

Reminder: 1eV = 1.6 x 10Reminder: 1eV = 1.6 x 10-19-19 J and h = 6.63 x 10 J and h = 6.63 x 10-34-34 Js Js

EM Radiation SourcesEM Radiation Sources1. Fundamentals of EM Radiation1. Fundamentals of EM Radiation

2. Light Sources2. Light Sources

3. Lasers3. Lasers

Optical SourceOptical SourceCharacteristicsCharacteristics

Ingle and Crouch, Ingle and Crouch, Spectrochemical AnalysisSpectrochemical Analysis

Douglas A. Skoog and James J. Leary, Douglas A. Skoog and James J. Leary, Principles of Instrumental AnalysisPrinciples of Instrumental Analysis, , Saunders College Publishing, Fort Worth, 1992.Saunders College Publishing, Fort Worth, 1992.

Continuum SourceContinuum Source Line SourceLine Source

Continuum + Line SourceContinuum + Line Source

Ingle and Crouch, Ingle and Crouch, Spectrochemical AnalysisSpectrochemical Analysis

Incandescent LampIncandescent Lamp

1. Glass bulb (or "envelope") 2. Low pressure inert gas 3. Tungsten filament 4. Contact wire (goes to foot) 5. Contact wire (goes to base) 6. Support wires 7. Glass mount/support 8. Base contact wire 9. Screw threads 10. Insulation 11. Electrical foot contact

www.wikipedia.org

Black-body RadiationBlack-body Radiation

In an ideal black body:In an ideal black body:

(() = 1, ) = 1, (() = 0, T() = 0, T() = 0) = 0

Because a black body is at thermal equilibrium, emission Because a black body is at thermal equilibrium, emission must equal absorption. must equal absorption.

Thus, black bodies are perfect absorbers and the most Thus, black bodies are perfect absorbers and the most efficient emitters possible.efficient emitters possible.

There are no ideal black bodies.There are no ideal black bodies.

Spectral Distribution of Emission is Characteristic of Spectral Distribution of Emission is Characteristic of the Temperature of the Blackbodythe Temperature of the Blackbody

As T increases, As T increases, maxmax decreases. decreases.

Donald McQuarrie, Donald McQuarrie, Quantum ChemistryQuantum Chemistry, University , University Science Books, Mill Valley, CA, 1983.Science Books, Mill Valley, CA, 1983.

www.wikipedia.org

Rayleigh – Jeans LawRayleigh – Jeans Law

4b ckT2

B 4

b ckT2 B

bBbB

Spectral RadianceSpectral Radiance (Jm(Jm-3-3ss-1-1))

The Ultraviolet CatastropheThe Ultraviolet Catastrophe

Approximate Blackbody ExpressionsApproximate Blackbody Expressions

Wien’s LawWien’s Law

kThceh

/

5

2b c2

B kThceh

/

5

2b c2

B

www.wikipedia.org

Resolved (inadvertently) Resolved (inadvertently) in 1900 by Max Planck.in 1900 by Max Planck.

Assumed atoms could Assumed atoms could only absorb or emit only absorb or emit discrete amounts of discrete amounts of energy.energy.

Planck’s Radiation Law:Planck’s Radiation Law:

1 - e

1

c

8 U

/kTh3

3b

h

1 - e

1

c

8 U

/kTh3

3b

h

Donald McQuarrie, Donald McQuarrie, Quantum ChemistryQuantum Chemistry, University , University Science Books, Mill Valley, CA, 1983.Science Books, Mill Valley, CA, 1983.

bUbU

Spectral Energy DensitySpectral Energy Density (Jcm(Jcm-3-3HzHz-1-1))

1

12B

/5

2

kThc

b

e

hc 1

12B

/5

2

kThc

b

e

hc

Wien’s Displacement LawWien’s Displacement Law

T

nmK 10 2.897

6

m

Eugene Hecht, Eugene Hecht, OpticsOptics, 1998., 1998.

Differentiate Planck’s Differentiate Planck’s Law with respect to Law with respect to and and set equal to zero to find set equal to zero to find mm (wavelength of (wavelength of

maximum irradiance):maximum irradiance):

Stefan-Boltzman LawStefan-Boltzman Law

MMbb = = TT44

= 5.6697 = 5.6697 10 10-12-12 W W··cmcm-2-2··KK-4-4

Integrate Planck’s Law to Integrate Planck’s Law to find the total emittance of find the total emittance of a black body:a black body:

Are you getting the concept?Are you getting the concept?

Suppose that we measure the emitted exitance from a small Suppose that we measure the emitted exitance from a small hole in a furnace to be 22.8 W/cmhole in a furnace to be 22.8 W/cm22. Compute the internal . Compute the internal temperature of the furnace.temperature of the furnace.

Recall: Recall: = 5.6697 = 5.6697 10 10-12-12 W W··cmcm-2-2··KK-4-4

Non-Ideal Sources – “Gray Bodies”Non-Ideal Sources – “Gray Bodies”

bw B T B bw B T B

Spectral radianceSpectral radiance Spectral radiance of a Spectral radiance of a true black bodytrue black body

Spectral Emissivity, Spectral Emissivity, :: Ratio of the spectral radiance Ratio of the spectral radiance of a true source to that of a black bodyof a true source to that of a black body

Accounts for Accounts for < 1 < 1

Eugene Hecht, Eugene Hecht, OpticsOptics, Addison-Wesley, Reading, MA, 1998., Addison-Wesley, Reading, MA, 1998.

= = (())

Corrections for Non-Ideal SourcesCorrections for Non-Ideal Sources

bw B T B bw B T B

TTww(() is the transmission factor of ) is the transmission factor of

the source envelopethe source envelope

www.edmundoptics.comwww.edmundoptics.com

Corrections for Non-Ideal SourcesCorrections for Non-Ideal Sources

Color Temperature (T)Color Temperature (T)

bw B T B bw B T B

T in is an adjustable parameterT in is an adjustable parameter

T is the temperature that the atoms experienceT is the temperature that the atoms experience

bBbB

The color temperature is the temperature of a black body whichmost closely matches the lamp's perceived color

Are you getting the concept?Are you getting the concept?

Calculate the spectral radiance of a tungsten lamp at 500 Calculate the spectral radiance of a tungsten lamp at 500 nm with a color temperature of 2700 K, nm with a color temperature of 2700 K, = 0.40, and T = 0.40, and T = =

0.92 in J/m0.92 in J/m33s.s. Recall: k = 1.38 x 10Recall: k = 1.38 x 10-23-23 J J··KK-1-1

and h = 6.63 x 10and h = 6.63 x 10-34-34 Js Js