1. to Optical Atomic Spectroscopy
Chapter 8
An Introduction
to Optical Atomic Spectroscopy

2. Three major types of spectrometric methods are used
to identify the elements present in samples of matter
and determine their concentrations: (1) optical spectrometry,
(2) mass spectrometry, and (3) X-ray spectrometry.
In optical spectrometry. discussed in this
chapter. the elements present in a sample are converted
to gaseous atoms or elementary ions by a process
called atomization. The ultraviolet-visible absorption,
emission, or fluorescence of the atomic species
in the vapor is then measured.

3. Sources of atomic spectra:
Atomic Spectroscopy
Atomic spectroscopy is based on absorption, emission,
or fluorescence by atoms or elementary ions.
Atomic spectra are obtained by measuring gaseous atoms or elementary ions that are converted from the components of a sample by a suitable heat treatment.
Sources of atomic spectra:
The emission, absorption and fluorescence spectra of gaseous atomic particles (atoms or ions) consist of well-defined narrow lines arising from electron transitions of the outmost electrons.

4. Optical Atomic Spectroscopy
Optical Spectrometry
Absorption
Emission
Fluorescence
Mass Spectrometry
X-Ray Spectrometry

5. 8A OPTICAL ATOMIC SPECTRA
8A-1 Energy Level Diagrams
The energy level diagram for the outer electrons of an
element is a convenient method to describe the processes
behind the various methods of atomic spectroscopy.
The diagram for sodium shown in Figure 8-1a
is typical. Notice that the energy scale is linear in units
of electron volts (e V). with the 35 orbital assigned a
value of zero. The scale extends to about 5.l4eV. the energy
required to remove the single 35 electron to produce
a sodium ion, the ionization energy.

7. FIGURE 8-2 Energy level diagram for atomic magnesium
FIGURE 8-2 Energy level diagram for atomic magnesium. The width of the lines between states
indicates the relative line intensities. Note that a singlet-to-triplet transition is considerably less
probable than a singlet-to-singlet transition. Wavelengths are presented in angstroms.

8. Spins are paired
No split
Spins are unpaired
Energy splitting 3p 3p 3s 3s 3s
Singlet ground state
Singlet excited state
Triplet excited state
FIGURE 8-3 Spin orientations in singlet ground and excited states and triplet excited state.

9. Atomic spectroscopy
Emission
Absorption
Fluorescence

10. Atomic Emission Spectra
at room temperature, all atoms of a sample are in the ground state; electrons can be excited by heat or electric arc or spark (nonradiative); the lifetime of the excited state is short; its return to the ground state is accompanied by the emission of a photon of radiation.

11. FIGURE 8-4 A portion of the flame emission spectrum for sodium.

12. Atomic Absorption Spectra:
absorption spectrum typically consists predominantly of resonance lines, which are the result of
transitions from the ground state to upper levels.

13. FIGURE 8-5 Energy level diagram for thallium showing the source of two fluorescence lines.

14. Atomic Fluorescence Spectra:
atoms in a flame can be made to fluoresce by irradiation with an intense source containing wavelengths that are
absorbed by the element. The observed radiation is most
commonly the result of resonance fluorescence; first radiation less transition to a lower energy state, then
fluoresce from there to a lower energy state. Thus a longer
wavelength than the resonance line will be observed.

15. FIGURE 8-6 Profile of an atomic line showing definition of the effective line width 1/2.

16. Line Broadening from the Uncertainty Effect
spectral lines always have finite widths because the lifetimes of one or both transition states are finite, which leads to uncertainties in the transition times and to line broadening as a consequence of the uncertainty principle;
when the lifetime of the two states approaches infinity,
then the breadth of an atomic line resulting from a transition
between the two states would approach zero.

20. Doppler Broadening
The l of radiation emitted or absorbed by a fast moving
atom decreases if the motion is toward a detector and
increases if the atom is receding from the detector.
magnitude: increases with the velocity at which the emitting or absorbing species approaches or leaves the detector;

22. FIGURE 8-7 Cause of Doppler broadening
FIGURE 8-7 Cause of Doppler broadening. (a) Atom moving toward incoming radiation sees wave crests more frequently and thus absorbs radiation that is actually higher in frequency. (b) Atom moving with the direction of radiation encounters wave crests less often and thus absorbs radiation that is actually of lower frequency.

23. Pressure Broadening
Pressure, or collisional, broadening is caused by collisions of the emitting or absorbing species with other atoms or ions in the healed medium.
These collisions produce small changes in energy levels
and hence a range of absorbed or emitted wavelengths.

24. 8A-3 The Effect of Temperature on Atomic Spectra
Temperature has a profound effect on the ratio between
the number of excited and unexcited atomic
particles in an atomizer. We calculate the magnitude of
this effect from the Boltzmann e4uation, which takes
the form

25. Here. Nj and No are the number of atoms in an excited
state and the ground state. respectively. k is Boltzmann's
constant (1.38 x J/K), T is the absolute
temperature. and Ej is the energy difference between
the excited state and the ground state, The quantities
gj and go are statistical factors called statistical weights
determined by the number of states having equal energy
at each quantum level. Example 8-2 illustrates a
calculation of Nj/No,

26. Effect of Temperature on Atomic Spectra
Temperature exerts a profound effect upon the ratio
between the number of excited and unexcited atomic particles in an atomizer;
Boltzmann equation: Nj/N0 = Pj/P0 exp(Ej/kT)
Pj, P0 are statistical factors that are determined by the
number of states having equal energy at each quantum level.

29. 8A-4 Band and Continuum Spectra Associated with Atomic Spectra

30. 8B ATOMIZATION METHODS
To obtain both atomic optical and atomic mass spectra,
the const it uents of a sample must he converted to
gaseous atoms or ions. which can then be determined
by emission, absorption, fluorescence, or mass spectral
measurements. The precision and accuracy of atomic
methods depend critically on the atomization step and
the method of introduction of the sample into the atomization
region.

31. 8C SAMPLE-INTRODUCTION METHODS
Sample introduction has been called the Achilles' heel
of atomic spectroscopy because in many cases this step limits the accuracy.

34. 8C-1 Introduction of Solution Samples
Pneumatic Nebulizers
Ultrasonic Nebulizers
Electrothermal Vaporizers
Hydride Generation Techniques

35. FIGURE 8-9 Types of pneumatic nebulizers: (a) concentric tube, (b) cross-flow, (c) frilled disk, (d) Babington.

36. Concentric Tube

37. Cross-flow

38. Fritted-disk

39. Line Broadening Uncertainty Effects Natural line width
Heisenberg uncertainty principle:
The nature of the matter places limits on the precision with which certain pairs of physical measurements can be made.
One of the important forms Heisenberg uncertainty principle:
t ≥ p156
To determine  with negligibly small uncertainty, a huge measurement time is required.
Natural line width

40. Babington

41. 8C-2 Introduction of Solid Samples
Direct Sample Insertion
Electrothermal Vaporizers
Arc and Spark Ablation
Laser Ablation
The Glow-Discharge Technique

42. FIGURE 8-10 A glow-discharge atomizer. (From D. S. Gough, P
FIGURE 8-10 A glow-discharge atomizer. (From D. S. Gough, P. Hanna ford, and R. M. Lowe 61 , Anal. Chem., 1989,1652.