Mechanism

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Mechanism
For elementary rxns onlyorder determined by
elementary rxn
key rxn, Ea56kJ
bimolecular
termolecular
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Unimolecular Reactions
Isomerization
Result of collisional activation
Bond Scission
Since 1960 people stop studying overall rexns and
studyelementary reactions. 1960--some
approximations describeover all system. Today
no approx because of computer modelsBig factor
often missing is energy mass transport. Very
important in reactor design.
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Flash photolysis
mild flow to replenish reagents
multiple reflection regioncould be heated or
cooled
uv photolysis
IR detector1µs response
193 nm ArF,XeF
break bond
H O atoms
Tunable IR probelaser (pulsed)
1017 photons/10ns
Absorption 1/cm1014-1015 radicals/cc
universal
sensitivity1011/cc
Example study deNOx reaction
acid rain, etc.
NO formed by burning N2 !
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de-NOx -- add NH3 to smoke stacks
NH2 NO --gt N2 H2O ?H0 -127 kcal/mol
--gt N2H(?) OH ?H0 - 3kcal/mol
--gt N2 H OH ?H0 -6 kcal/mol
Rate of disappearance known, but not branching
measured by LIF of NH2
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1. Measure NH2 NO--photolyze NH3/NO
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2. Branching ratio--intensity of H2O lines
Water is formedafter a delay. Fromsecondary
rxn?
So maybe H2O is formed
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HNO2--gtOH NO
k is known
Plus that from NH2NO
Only from NH2NO