spectroscopy 101 arkansas 2-day october 2013 lisa mcgaw osu [email protected]
TRANSCRIPT
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 = λνRadio Microwave Far IR IR Visible UV X-ray
10 m 1 x 10-2 to 5 x 10-4 m
5 x 10-4 - 1.5 x 10-5m
1.5 x 10-5 - 7 x 10-7 m
7 x 10-7 to 4 x 10-7 m
4 x 10-7 to 1 x 10-7 m
1 x 10-7 to 1 x 10-16 m
Nuclei(nmr)
Electron spin (esr)
Electron spin(esr)
Molecular vibrations (IR)
Valence electrons (UV-Vis)
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)
https://en.wikipedia.org/wiki/Infrared_spectroscopy
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 Absorbed Red – Orange Yellow-Green Blue-Violet Color Transmitted
Blue, Green Purple Red, 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