Spectroscopy

Pregunta	Respuesta
Spectroscopy	Spectroscopy is based on the measurement of absorption or emission of electromagnetic energy by a sample!
This may be by molecules (molecular) or atoms (atomic)	Radiation energy includes; visible light,UV radiation, infra red, radio f requency, xrays
Introduction to Spectroscopy techniques	The most widely used techniques are based on visible light, UV radiation, IR radiation and NMR becoming more widely used. Each type of technique is distinct in that they monitor different types of molecular and or atomic transitions within the molecule/ atom of the sample
Basic Principles	Electromagnetic radiation is a form of energy that shows both electrical and magnetic characteristics. Electromagnetic radiation can be considered to be a stream of separate groups of electromagnetic waves (photons) The energy that is associated with electromagnetic radiation is related to the waveform.
Electrical field	At right angles of the electrical field waveform there is the magnetic field which oscillates at the same frequency. From this we can define wavelength and frequency.
Wavelength	the distance between successive peaks measured in (nm)
frequency	the number of successive peaks that pass a given point in 1 second
Energy relationships	Associated energy of electromagnetic radiation is directly related to frequency and so is inversely related to wavelength
Equation	E = hv = hc/wavelength
Photons	The particles of energy moving through space with wavelike properties are called photons. In the energy relationships, E is the energy of the photons associated with a particular wavelength and so frequency. Photons are discrete packets of energy
Energy in molecules and atoms	To appreciate absorption of energy by atoms and molecules it is necessary to consider energy distribution within atoms and molecules. Energy content of matter is quantized. Internal energy of atoms and molecules does not vary in a continuous manner. They are normally in state of lowest energy.
Internal energy of molecules and atoms	energy associated with electrons energy associated with vibrations energy associated with rotations Emol= E(elect)+E(vibr)+ E(rot) In atoms, no vibrational or rotational energy involved.
Alteration	Internal energy levels can be altered by absorption or emission of energy as radiation (photons) Any atoms or molecule can only exist in a limited number of "permitted" energy levels. Any changes in energy level must but in definite steps.
Photo slide here.	Only photons of a particular frequency and wavelength will be selectively absorbed or emitted. The set of available or "permitted" energy levels for any given atom or molecule will be distinct for that species.
P2	Each element, or compound will have characteristic "permitted" energy levels and so absorb and emit characteristic photons. So the wavelength and or frequency radiation absorbed or emitted by a species will identify- qualitative spec.
Quantitative spectroscopy	Measurement of the amount of radiation involved at the characteristic wavelength or frequency gives information on the number of absorbing or emitting atoms or molecules.
On absorption of photons,	the increase in internal energy of a molecule is accommodated in the vibrational, rotational and electric energies. Absorption of electronic energies cause transition of the electron between orbitals.
Flame atomic spectroscopy	The liquid sample is aspirated into a spray chamber where it is formed into a fine spray of droplets - nebulisation
The spray and fuel gases are carried to the flame.	The solvent is immediately evaporated and salt particles vaporised.
The molecular associations in the vapour are broken - molecular association to form some free ground state atoms	some of the atoms formed in the flame may gain the correct amount of energy to be raised to the next energy state from the flame. some may be ionised by majority will remain in ground state
Remember...	Atoms of a particular element absorb only a specific quanta of energy related to promotion of the outer electron to excited states.
specific energy	As such, the energy that atoms of each element can absorb is different to all other elements.
Characteristic energy	The energy is specific to the energy required for transitions of that element.

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