A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
ABSORPTION SPECTROSCOPY
A type of spectroscopy where the amount of radiation, of a particular wavelength, absorbed by the sample being analysed is measured. The wavelength that is absorbed depends of the molecule as different electronic transitions and therefore absorption occurs at different wavelengths.
BEER-LAMBERT LAW
An equation relating absorbance, path length, molar absorption coefficient and concentration of the sample: A = ecl
CHROMOPHORE
A chromophore is a functional group that is responsible for absorption e.g. an alkene absorbs at lmax=177nm.
CONJUGATION
An extended series of alternating single and double/triple bonds which causes the p orbitals to overlap. Conjugated systems tend to show absorption in the visible region
DEUTERIUM
An isotope of hydrogen. Deuterium has 1 proton, 1 electron and 2 neutrons where Hydrogen has 1 neutron.
DOUBLE BOND
A bond where (e.g. in Carbon) the s orbital and two of the p orbitals hybridize to give 3 sp2 orbitals which form sigma, s, bonds (e.g. with hydrogen or carbon). The remaining p orbital forms a pi, p, bond with another sp2 hybridized carbon:
The range of electromagnetic energy with wavelengths ranging from 105m (radio waves) to 10-14m (gamma radiation). In between these extremes is the infrared, visible, ultraviolet and X-ray regions.
FLUORESCENCE
Fluorescence occurs when an electron is promoted from the ground state to the excited state. When the energy is lost from the electron, it is first of all lost by heat through vibrational relaxation then by giving out light (fluorescing) when it returns to the ground state.
HOMO
Highest Occupied Molecular Orbital. The orbital in a molecule where the highest energy level is occupied by an electron at absolute zero.
LUMO
Lowest Unoccupied Molecular Orbital. The lowest energy orbital which is not occupied by an electron at absolute zero.
A measure of the amount of radiation absorbed per unit concentration of the sample as the equation can be rearranged to: e = A / cl (Beer-Lambert Law). This value is a constant for a particular substance.
MOLECULAR ORBITALS
Orbitals that result from the interaction of atomic orbitals when bonds are formed. Bonding orbitals are lower in energy than the original atomic orbitals, anti-bonding orbitals are higher in energy and non-bonding orbitals are of equal energy.
PHOSPHORESCENCE
This is a very similar process to fluorescence but the emission of radiation continues after the source of excitation is removed. This is due to intersystem crossing from the singlet state to the triplet state which happens slowly.
The method of producing and analyzing data to allow determination of the structure of molecules.
TRANSMITTANCE
The amount of radiation which passes through the sample i.e. is not absorbed. Amount of radiation going in/amount of radiation that passes through. When this fraction is multiplied by 100, the value obtained is the percentage transmission.
ULTRAVIOLET REGION
The region of the electromagnetic spectrum which has wavelengths between 400-4nm. The UV region is split into three more regions: near UV (400-300nm), far UV (300-200nm) and extreme/vacuum UV (less than 200nm). The latter is know as the vacuum UV region as the radiation is absorbed by oxygen. This means that if vacuum UV radiation is being used then the apparatus must be evacuated.
VISIBLE REGION
The region of the electromagnetic spectrum (700-400nm) which the human eye is sensitive to and sees as white light and colours.
WAVELENGTH
The measurement of waves from peak to peak e.g. radio waves have a wavelength of up to 10km where gamma radiation have wavelengths as short as 10-14m (0.00000000000001m).
