Week 2 Flashcards
What is photolysis?
When chemical bonds in a molecule are broken down by an incident photon
Equation for photolysis reaction?
X+hv –> Y+Z
What does AB* represent?
Excited activated complex that reacts rapidly with A&B or C&D
Why is a third body (M) needed ?
To stabilise the excited complex of AB*
Common three body reaction equation?
A+B+M –> AB+M
What can M be made up of?
Inert molecules (O2 or N2)
Rate constants of 3 body reaction?
k1[A][B] = k2[AB] + k3[AB][M]
Definition of a radical?
A chemical species with an unpaired electron in the outer (valence) shell
What is needed to form radicals from non radicals?
An external energy source
Initiation step- radical formation
nonradical + hv –> radical + radical
What does hv represent?
Light energy
Propagation step- radicals
Radical + Non radical –> radical + non radical
What is a branching reaction?
When a new non radical may be photolysed
Termination step equation - radicals
Radical + Radical (+M) –> nonradical +nonradical
What is the hydroxyl radical (OH) responsible for?
The removal of many pollutants
Hydroxyl radical - equation 1- Initiation step
O3+hv → O2 + O(1D)
Hydroxyl radical- equation 2- propagation 2
O(1D)+M → O + M
Hydroxyl radical - equation 3- propagation step
O(1D) + H2O → 2OH
What is actinic flux?
Photons entering slab of unit area atmosphere per unit time from any direction (photons cm-2s-1)
What do we assume in a steady state of AB*?
Production=Loss
