Instant Notes: Analytical Chemistry

194 Section E – Spectrometric techniques

Rotational levels

3

2

1

0

3

1

4

2

0

Vibrational

levels

First excited

electronic state

Ground electronic state

Rotational levels

3

2

1

0 2 1

1

2

4

3

3

0

1

1

0

3

4

0

Vibrational

levels

Energy

Fig. 5. Energy level diagram for a molecule.

Although the technique of mass spectrometry does not normally involve

electromagnetic radiation, molecules or atoms are ionized and dissociated by

the removal of electrons using high-energy techniques (see Topic E14). The ions

are then dispersed, detected and displayed as a mass spectrum. The information

given by measurements using mass spectrometry is helpful both in combination

with atomic emission spectrometry (see Topic E5) and in molecular structure

elucidation, where it is used in conjunction with other molecular spectrometric

techniques (see Topic F2). For this reason mass spectrometry is often included in

a discussion of spectrometry.