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

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.

ULTRAVIOLET-VISIBLE SPECTROSCOPY: Electron Spectroscopy THE UV-Visible spectrum ranges approximately from 150-750nm. 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.

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.

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.

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

IR Spectrum of CO2 O = C = O O = C = O

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)

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

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

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

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

Mass Spectrometry - Molecules

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

Mass Spectrometer MS Library Heroin MS of Unknown

Mass Spectrometer MS Library Cocaine MS of Unknown

Mass Spectrometer MS Library Caffeine MS of Unknown

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