How to Determine the Wavelength to Cleave O-H Bonds in Water?

[member 392791]

Hello,

I was wondering how I could go about finding the wavelength of light that would cleave the O-H bonds of a water molecule.

I looked up the bond dissociation energy of the O-H bond, and it is 460 kJ/mole.

Now, since there are two O-H bonds, it should be twice as much, 920 kJ/mole.

Would the correct equation to use to find the wavelength to dissociate the bonds be

E = hc/λ?

That E is usually the energy to promote an electron to a higher energy level, but I wonder if it can be used in this case. When I did it, I found the wavelength to be on the order of 10^-25 meters, so something with a far lower wavelength than even a gamma ray. Is cleaving a chemical bond using radiation feasible?

 

[sjb-2812]

It may be better to consider bond strength per molecule, not per mole. But yes, radiation can be used to cleave bonds.

 

[Yanick]

Cleaving bonds with EM radiation is possible, but not for every case and it is not always practical.

For your specific example you can look for papers dealing with water radiolysis. Gamma irradiated water is known to make radicals the infamous one being the hydroxyl radical, which is formally a homolytic cleavage of an OH bond.

More terms to use to learn about this type of thing would be photochemistry.

 

[member 392791]

I am trying to figure out if I can use photolysis to break down water or some other compound (hydrogen peroxide) to form H2 and O2 without the radicals and other side products. Anyone have some literature of what I can do for this and what wavelength I need to cleave the bonds.

 

[member 392791]

Also, is that calculation the proper way to find the wavelength with enough energy to cleave the bond. I am not sure if that just has to do with promoting electrons to higher energy orbitals.