Lecture 11

Atomic absorption

Only photons of one specified wavelength areabsorbed

hchE

Ground state

Excited state

Width

Dopplerc

v

Speed of light 300,000,000 m/s

Velocity of a particle >1000 m/s

collisions Approximately as Doppler

Both effects increase with the temperature and

decrease with the size of the molecule/atom

Multiple energy levels

Width is around 0.01-0.001 nm in visible area

Energy levels of ground state

Energy levels of excited state

Energy sublevels

A primitive rule:

Molecular spectra - wide bands

Atomic spectra - narrow lines

Na 1s22s22p63s1

E(eV)

E=h/c

kT

E

eN

N

~0

N0

N* Flame Temperature

Butane-air <2200Acetylene-air 2400-2600

Acetylene-N2O 2900-3100

Acetylene-O2 3300-3400

Line

Monochromator bandwidth

Auxilary oxidant

Oxidant

Sample capillary

Nebulizer

Adjustingknob