red, resonance Raman, circular dichroism, magnetic circular dichroism spec-
troscopies, and many others are not discussed here. Students are referred to
analytical and instrumental texts^2 for more information on all methods, dis-
cussed here or not. The volumes listed in reference 1 are especially helpful
because they emphasize instrumental methods applied to the analysis of bioin-
organic systems.
3.1.2 Spectroscopy,
Students will be familiar with the absorption or emission of electromagnetic
radiation as the basis for spectroscopic methods. Electromagnetic radiation
itself is perceived as mutually perpendicular oscillating electric and magnetic
fi elds. The total energy of the radiation, which has a number of components,
is determined by the relationship shown in equation 3.1 :
Eh
hc
total== =ν EEEEtranslation+rotation+vibration+electron s
λ
ppin nuclear spin
nuclear levels
+
++
E
E ... (3.1)
where
h = Planck ’ s constant = 6.626 × 10 − 34 Js
c = the speed of light = 3 × 10^8 m s − 1
ν = the frequency of light in s − 1 (Hz)
λ = the wavelength of light in meters (m)
Atomic and molecular energy levels represent specifi c quantum states (ground
and excited) illustrated in Figure 3.1. Transitions between these states, which
may be caused either by energy absorption or energy emission, are responsible
for physical method observations. Some details are shown in Figure 3.2. Energy
transition examples include:
Figure 3.1 Energy transition (absorption or emission) between ground and excited
states.
hν
excited state
ground state
INTRODUCTION 77
