We present quantum dynamical calculations that describe the rotational excitation of H _ { 2 } O due to collisions with H atoms .
We used a recent , high accuracy potential energy surface , and solved the collisional dynamics with the close–coupling formalism , for total energies up to 12 000 cm ^ { -1 } .
From these calculations , we obtained collisional rate coefficients for the first 45 energy levels of both ortho– and para–H _ { 2 } O and for temperatures in the range T = 5–1500 K. These rate coefficients are subsequently compared to the values previously published for the H _ { 2 } O / He and H _ { 2 } O / H _ { 2 } collisional systems .
It is shown that no simple relation exists between the three systems and that specific calculations are thus mandatory .