Jump to content

MRDlhl17

From ChemWiki

Molecular Reaction Dynamics: Applications to Triatomic systems

Louise Li

EXERCISE 1: H + H2 system

On a potential energy surface diagram, how is the transition state mathematically defined? How can the transition state be identified, and how can it be distinguished from a local minimum of the potential energy surface?


Report your best estimate of the transition state position (rts) and explain your reasoning illustrating it with a “Internuclear Distances vs Time” plot for a relevant trajectory.


Comment on how the mep and the trajectory you just calculated differ.


p1/ g.mol-1.pm.fs-1 p2/ g.mol-1.pm.fs-1 Etot Reactive? Description of the dynamics Illustration of the trajectory
-2.56 -5.1
-3.1 -4.1
-3.1 -5.1
-5.1 -10.1
-5.1 -10.6

Complete the table above by adding the total energy, whether the trajectory is reactive or unreactive, and provide a plot of the trajectory and a small description for what happens along the trajectory. What can you conclude from the table?


Given the results you have obtained, how will Transition State Theory predictions for reaction rate values compare with experimental values?


EXERCISE 2: F - H - H system

By inspecting the potential energy surfaces, classify the F + H2 and H + HF reactions according to their energetics (endothermic or exothermic). How does this relate to the bond strength of the chemical species involved?


Locate the approximate position of the transition state.


Report the activation energy for both reactions.


In light of the fact that energy is conserved, discuss the mechanism of release of the reaction energy. Explain how this could be confirmed experimentally.


Discuss how the distribution of energy between different modes (translation and vibration) affect the efficiency of the reaction, and how this is influenced by the position of the transition state.