1. Chapter 12: Part 2 Molecular Spectroscopy
12.5 – Mass Spectrometry
12.6 – Radiochemical Analysis

2. Using the behavior of electrons in bonds…again.
-Molecules are groups of atoms bonded together. -Bonds are interactions between the electrons of two atoms. -The electrons in a bond can behave the same way electrons do in an atom when exposed to light/radiation (just like in Part 1) Chemical Bond: When electrons hold together the nuclei of two atoms Antibonding: When electrons are pushed away from each other leaving the nuclei of the atoms to repel each other. Molecular Orbitals: When a bond forms, a new wave-like property will result from the bond. Not just the waves of an atoms anymore.

3. ULTRAVIOLET-VISIBLE SPECTROSCOPY: Electron Spectroscopy
THE UV-Visible spectrum ranges approximately from nm.
Referred to as electron spectroscopy
because there is enough energy to
move the electrons between energy
levels (ground state --> excited state,
etc.)
The wavelengths emitted & the intensity of the peaks (height) determine the identity & the amount of the substance.

4. Organic Molecules: Functional Groups
Functional Groups are small groups of atoms/components that are bonded to an organic molecule. For example  OH will make a hydrocarbon an alcohol  COOH will make an organic acid *These groups will change the properties of the molecule AND result in a a unique spectroscopy pattern since they absorb specific wavelengths of light. *Knowing the functional group will help I.D. the unknown substance *The amount of light absorbed give quantitative data.

5. Color & Forensics
Individuals perceive (see) color in different ways. The most accurate way to describe a color would be to identify their wavelengths. Ex. Two different reds can be distinguished by using 510 nm and 525 nm to describe them more accurately. Complementary Color: The color perceived as opposed to the color absorbed by an object.

6. INFRARED SPECTROSCOPY (IR) Vibrational Spectroscopy
Different types of bonds have characteristic regions of the spectrum where they absorb
What does this spectrograph show?
-Transmission of IR radiation
-Vibrational waves of the
bonds in the molecules

7. IR Spectrum of CO2
O = C = O
O = C = O

8. Infrared Spectroscopy
Forensic Applications of Infrared Spectroscopy
Use of computer databases of IR’s of known compounds
-Analyzing Alcohol - The breath is tested with a mechanism similar to a breathalyzer
(chemical oxidation) but uses the infrared absorptions of alcohol.
-Identify AND verify an unknown substance (drugs)
-Analysis of fiber (compared under microscope then
verified through IR Spec.)
-Paint & ink analysis (individual layers of paint are
analyzed)

9. MICROWAVE, TERAHERTZ, X-RAY
Microwave & Terahertz – Long wavelength technology *Used for imaging as *Terahertz radiation passes through… clothing, wood, plastic, fog and ceramics. *Terahertz radiation does not pass through… Metal, water, certain chemicals *Visualization of concealed weapons through clothing, sealed envelopes, packages

10. MASS SPECTROMETRY (MS)
Sample molecules are ionized by an electron beam to cations (+1 by “knocking off” one electron) which are then deflected by magnetic field for ions of the same charge. The angle of deflection is proportional to the ion’s mass

11. Magnetic field deflection (quadrupole MS)
Mass Spectrometer
Magnetic field deflection (quadrupole MS)

12. MASS SPECTROMETRY (MS)
Mass Spectrometry identifies molecular mass and how molecules fall apart into fragments
Mass
Spectrum
Mass
Spectrum
Mass
Spectrum
Int.
Int.
Int. Cl C P 35 31 12 37 13
mass number (amu)
mass number (amu)
mass number (amu)
35Cl: 75% abundant
37Cl: 24% abundant
12Cl: 98.9% abundant
13Cl: 1.11% abundant
31P: 100% abundant

13. Mass Spectrometry - Molecules

14. Mass Spectrometer
Unknown white powdery substance ingested by unconscious patient.
What do you do? Is it Heroin, Cocaine, Caffeine?
Mass Spectrum of Unknown Compound

15. Mass Spectrometer
MS Library
Heroin
MS of Unknown

16. Mass Spectrometer MS
Library
Cocaine
MS of Unknown

17. Mass Spectrometer
MS Library
Caffeine
MS of Unknown

18. Mass Spectrometer Mass Spectrum Caffeine
Unknown white powdery substance ingested by unconscious patient.
What do you do?
Mol. Wgt
= 194
Mass Spectrum
Caffeine