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Lecture notes of 8 pages for the course Techniques For Biological And Chemical Sciences at QMUL
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General spectroscopy and IR spectroscopyLearning objectives
1. Define spectroscopy
2. Describe the fundamental properties of light
3. Define the relationship between frequency and wavelength
4. Define the relationship between frequency and energy
5. Describe energy levels in a molecule
6. Relate the energy of light absorbed with the energy transitions of a molecule
7. List some spectroscopic methods and their related energy transitions
8. Describe the physical principle behind IR spectroscopy
9. Review and evaluate the use of IR spectroscopy to determine secondary structure
Fundamentals of spectroscopy
Measurement of the interaction of light with a substance, typically the absorption (or fluorescence) of light by the
molecule
The spectrum is a plot of the absorbance of light vs the wavelength
All spectroscopic techniques contain a light source, sample and detector
What is light?
An oscillating electric (E) and magnetic field (B)
Light often called electromagnetic radiation
Light has both wave-like and particle-like (quanta of energy of photon) properties
Visible region of light can be seen by the naked eye
Frequency, wavelength and speed
Light has:
- Speed (c) (300,000,000 m/s),
- Frequency ( ν ¿
- Wavelength ( λ )
Frequency = speed/ wavelength
- Frequency is inversely proportional to wavelength
- The constant, C is the speed of light
- High frequency = short wavelength
, Spectrum of light
Range of wavelength
Microwaves are constantly going through us
Radio waves are broad
Gamma rays are smaller than the size of an atom, which allows gamma rays to interact with atoms
Different wavelengths of light have different energies
Energy = Planks-Constant x Frequency
- (6.62 *10-32 J s)
The energy of light is proportional to the frequency or inversely proportional to the wavelength of light i.e. the longer
the wavelength the lower the energy
Light can be described in terms of its energy but more typically in terms of frequency (Hz or MHz)
Wavelength ( m or nm), or as wave-number (cm-1)
Wavenumber = 1/wavelength (wavenumber is the reciprocal of wavelength
High frequency = high energy
Frequency is inversely proportional to wavelength
Electromagnetic spectrum
X-rays have high energy and short wavelengths
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