Determine the dissociation energy with an electron beam

[wrum]

Hi!

If you use an electron beam on hydrogen gas and when the energy of the beam is 22 eV H+ start to appear, how can you calculate the dissociation energy of H2 using that information?

I've tried: 22 eV = D + "ionization energy of a H atom" etc, but couldn't make it add up.

I would be very thankful if someone could help me with this! =)

[Bob S]

I think the molecular binding energy is about 3.6 eV, and the hydrogen atom ionization energy is 13.6 eV, leading to about 17 eV for producing ions by electron impact. See

http://physics.nist.gov/cgi-bin/Ionization/graph_new.pl?element=H2.0

Bob S