spectroscopy 101 arkansas 2-day october 2013 lisa mcgaw osu lmcgaw@me.com

SPECTROSCOPY 101

Arkansas 2-DayOctober 2013Lisa McGaw OSUlmcgaw@me.com

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