New, unexpected, and dominant mechanisms in the hydrogen exchange reaction

Stuart J. Greaves, Daniel Murdock, Eckart Wrede, and Stuart C. Althorpe,
[1] J. Chem. Phys. 128, 164306 (2008).

We have studied the H + D2(v = 0, j = 0) → HD(v', j') reaction using the quasi-classical trajectory (QCT) methodology. Please refer to the above paper for more detail.

Characteristic trajectories showing the new reaction mechanisms in H + D2(v = 0, j = 0) collisions at Ecol = 1.85 eV

5 million trajectories for H + D2(v = 0, j = 0) collisions were propagated at a collision energy of Ecol = 1.85 eV. Reactive trajectories for the HD(v' = 0, j' = 0−1) product quantum states were analysed in detail to highlight the new reaction machanisms.

Figure 1 below (adapted from [1]) shows the striking correlation between the impact parameter, b, of the H atom before the collision and the deflection angle, Θ, of the product HD molecule. Ref. 1 describes this and the additional correlation between b and the initial orientation of the D2 molecule with respect to the incoming H atom in more detail. Trajectories with low impact parameters are deflected sideways into the backward hemisphere (the H atom, now in the HD molecule, turns around) whereas trajectories with increasing impact parameters are more and more forward scattered (the HD molecule carries on in the same direction as the incoming H atom). Most trajectories are scattered on the near side, i.e., into the same hemisphere as the incoming H atom.

Click on the links below or on the numbered areas on Figure 1 to start the corresponding trajectory movies.

b / ÅΘ / deg
Traj 10.0276141.6
Traj 20.2572114.0
Traj 30.0109−133.1
Traj 40.2556−164.5
Traj 50.3484178.9
Traj 60.6736132.9
Traj 70.942281.6
Traj 81.19976.6
Traj 91.2616−42.0
Traj 100.789114.3
Trajectory 1: ear region Trajectory 2: ear region Trajectory 3: far-side spiral region Trajectory 4: far-side spiral region Trajectory 5: near-side spiral region Trajectory 6: near-side spiral region Trajectory 7: near-side spiral region Trajectory 8: near-side spiral region Trajectory 9: near-side spiral region Trajectory 10: sickle region
Correlation between deflection angle and impact parameter
Figure 1: Deflection angle, Θ, versus impact parameter, b, for HD(v' = 0, j' = 0−1) products from QCT calculations of H + D2(v = 0, j  =0) collisions at a collision energy of 1.85 eV. The labels refer to the regions ...

Reaction mechanisms RDSG home E Wrede home

Eckart Wrede, 10 Apr 2008 [under construction]