photon + H2 collision

[physgirl]

So if a H2 molecule collides with and absorbs a photon of wavelength around 60nm, I find the final velocity of H2 molecule (assuming momentum's conserved in collision) to be around 3.5 m/s, which I think is very small... I would have thought that since the wavelength of the photon is so small, the energy of it is pretty high, which means H2 should move much faster than just 3.5 m/s after the collision... it just doesn't make sense to me conceptually, I guess. Is there something wrong with my logic?

[Meir Achuz]

Only in questioning your answer, which is correct.
The velocity is slow because H2 is so massive.
Preconception is the mother of confusion.

[olgranpappy]

Hi. Just curious. What text did this question come out of? Are there any further questions about the internal excitation energy of the H2 molecule after the collision?