Synchrotron Methods Flashcards
What leads to synchrotron radiation?
Electrons when pushed away from their linear path experience a change in momentum this leads to emission of synchrotron radiation (if control speed and path get monochromatic radiation electron experience chang in momentum if you have enough radiation can generate x rays)
Where does synchrotron radiation occur?
Known to occur in outer space where strong magnetic fields are present
How can synchrotron radiation be generated on Earth?
By accelerating electrons in vacuum and then knocking them off path, electron speed and x ray colour are correlated, electron speed and the magnitude of change in momentum allow brightness of x ray light (down to IR) and frequency to be controlled
Processes in synchrotron methods?
Synchrotron radiation offers IR to e-ray energy spectrum, x rays energy can be scanned into the absorption edge
Process 1: x ray absorption when the edge is reached
Process 2: primary electron excitation/emission
Process 3: secondary electron or x ray emission
Detection of x rays is more difficult therefore secondary electron detection to give spectrum
What is XAS?
X ray absorption spectroscopy
what is XAFS?
X ray absorption fine structure (neighbouring atom energy within atoms)
What is EXAFS?
Extended x ray absorption fine structure (distance between atoms)
What is NEXAFS?
Near edge extended x ray absorption fine structure (how to transform spectrum with pair distribution function, neighbouring info can be found)
What is XANES?
X ray absorption near edge spectroscopy
What does XANES allow?
Xanes goes beyond atomic orbitals and allows access to molecular orbitals and near edge states, bond the near edge states are the neighbouring atoms
How does XANES pick up geometries and redox states?
Distinct XANES patterns are seen for Co complexes or for Ni complexes with different geometries, change in ligand will also have a specific patter, changes in redox states are also cealrly distinguishable
What is EXAFS scattering?
The out going photo electrons can be considered a wave, constructive and destructive interference depends on neighbouring atoms and geometries, this is the ‘waviness’ in the EXAFS region, can transform into the distance between atoms
How does EXAFS resolve coordination geometry?
The Fourier transformed x ray absorption data shows bond distance information, Fourier filtering and back Fourier transformation allows coordinations shells to be separated, distinct bits of information superimposed on one spectrum
What are the unique properties synchrotron light has?
High brightness Wide energy spectrum Specific elements Highly polarised Time structured emission
High brightness of synchrotron light?
Synchrotron light shunners of thousands of times more intense than that from conventional x ray tubes and is naturally highly collimated
