SPECTROSCOPY 101 Arkansas 2-Day October 2013 Lisa McGaw OSU
Spectroscopy Spectroscopy –(In plain English) - a technique used to help us understand the molecular structure of matter by observing motion in response to the absorption of energy
TYPES OF SPECTROSCOPY IR UV-VIS MASS SPEC PES Many others – microwave, esr; x-ray; NMR; Raman; atomic absorption, etc.
Electromagnetic Radiation and Transitions E = hν and c = λν RadioMicrowaveFar IRIRVisibleUVX-ray 10 m1 x to 5 x m 5 x x m 1.5 x x m 7 x to 4 x m 4 x to 1 x m 1 x to 1 x m Nuclei (nmr) Electron spin (esr) Molecular vibrations (IR) Valence electrons (UV-Vis) (Mass spec) Inner electrons (PES) (Mass spec)
IR Spectroscopy 1.D (LO 1.15) Transitions in molecular motion – rotational, vibrational and electronic (low energy to high energy) Detect presence of different types of bonds Useful for identification and structural analysis of organic and inorganic compounds.
Dichloromethane near IR
UV- Vis Spectroscopy 1.D (LO 1.15 and LO 1.16) (SP 4.1, 4.2, 5.1 and 6.2) Transitions in electronic energy levels Used to probe electronic structure Molecules absorb UV or Visible light A = abc (absorption directly related to concentration)
How Do the Colors Relate? UV region – not visible to our eyes Visible region – ROYGBIV Low energy higher energy Color AbsorbedRed – OrangeYellow-GreenBlue-Violet Color Transmitted Blue, GreenPurpleRed, orange, yellow
UV Spectroscopy
Blue Dye
Standard Curve
Mass Spectroscopy 1.D (LO 1.14) (SP 1.4 and SP 1.5) Demonstrates direct evidence of different isotopes from the same element Average atomic mass estimated from mass spec data Solid, liquid or gas sample is ionized; Ions are separated according to mass to charge ratio
Isotopic Data for Bromine (web elements.com)
PES Spectroscopy 1.B (LO 1.7* also LO 1.5, 1.6, 1.8) (SP 1.5, 5.1, 6.2) Photoelectric effect – incident light ejects electrons Energies provide evidence for shell model Intensity of signal implies number of electrons at that energy level
PES Spectroscopy