NO2 is a yellow gas responsible for the brownish haze that builds up periodically over large cities like Los Angeles. NO2 readily decomposes to NO + O in sunlight (a reaction called photodissociation ).
NO2 + hv -> NO2* -> NO + O
ground state excited state
You can assume the relevant part of the molecular orbital diagram for NO2 (HOMO and LUMO) closely resembles the diagram for O3, shown above (although the number of valence electrons is not the same).
b. Which electronic transition (movement of electron from one orbital to another) accounts for the yellow color?
c. Explain why the excited state molecule is more likely to undergo photodissociation than the ground state.
Solution
Nitrogen dioxide has one unpaired electron which makes very reactive.nitrogen dioxide gas is also very toxic. When heated to higher temperatures its color becomes dark and eventually brown gas. When it is cooled down, the color becomes yellow then more paler and subsequently colorless. The color of nitrogen dioxide gas is consequence of absorption of light in 400- 500 nm region. The brown color is complimentary color of green - blue color which is absorbed at 400- 500nm. The transition is likely to be n??* .
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NO2 is a yellow gas responsible for the brownish haze that builds up p.docx
1. NO2 is a yellow gas responsible for the brownish haze that builds up periodically over large
cities like Los Angeles. NO2 readily decomposes to NO + O in sunlight (a reaction called
photodissociation ).
NO2 + hv -> NO2* -> NO + O
ground state excited state
You can assume the relevant part of the molecular orbital diagram for NO2 (HOMO and LUMO)
closely resembles the diagram for O3, shown above (although the number of valence electrons is
not the same).
b. Which electronic transition (movement of electron from one orbital to another) accounts for
the yellow color?
c. Explain why the excited state molecule is more likely to undergo photodissociation than the
ground state.
Solution
Nitrogen dioxide has one unpaired electron which makes very reactive.nitrogen dioxide gas is
also very toxic. When heated to higher temperatures its color becomes dark and eventually
brown gas. When it is cooled down, the color becomes yellow then more paler and subsequently
colorless. The color of nitrogen dioxide gas is consequence of absorption of light in 400- 500 nm
region. The brown color is complimentary color of green - blue color which is absorbed at 400-
500nm. The transition is likely to be n??* .
