Talk:MRD:fp1615 molecular reaction dynamics

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Excellent work! Basically all the questions were answered correctly. Your writing style is on point, the structure is clear and I could follow your argumentation throughout. Here are a couple of pointers on how to improve further:

Answers to questions

Properties of the TS I see you invested considerable effort in this answer, but unfortunately it is not quite right. I think you switched the < and > around in your equations. Let me explain: A TS is a maximum in one direction and a minimum in the other. So you're right in saying the partial derivatives are both 0. Let's assume x is the direction along which we find a maximum and the minimum is along y. Then $f_{x x} < 0$ & $f_{y y} > 0$ . You know this from 1D calculus: If you find an extreme point that's curved negatively, the points on either side of the extreme must have lower functional values and you have a maximum (and the other way round for minima). This gives us $f_{x x} f_{y y} < 0$ . Now $f_{x y}^{2} > 0$ since it is a square and $f_{x x} f_{y y} - f_{x y}^{2} < 0$ for a saddle point. You may have noticed that this derivation of the discriminant actually assumes the minimax property of the TS, so it is actually easier to test for the saddle point by using this assumption rather than using the discriminant itself. There are however saddle points that aren't minimax points, then $f_{x x} f_{y y} > 0$ and $f_{x y}^{2} > f_{x x} f_{y y}$ . These don't look like saddles, but more like terasses.

Unfortunately there are two types of TS theory out there. The one you quoted is the Eyring theory. It is mainly based on thermodynamic arguments, which themselves are statistical (that's why we can talk about equilibria). Do you think this is an appropriate description of the system at hand?

Experimental verification of release of vibrational energy What specific aspect of IR allows you to infer the occupation of vibrational levels? Could you draw this out on a diagram? What about the role of harmonic and anharmonic oscillators?

Grammar

You used articles in front of capitalised nouns, such as "The Hammond's postulate". Omit the "the" before such nouns.

Introduction

In the introduction you state that every successful reaction has to go over the TS, but later on you show the opposite. It would be good to indicate in the introduction that you will contradict this widely accepted fact and later on, when you actually disprove it, remind people of the original statement in the introduction. This emphasize your input in the work and your critical evaluation of the literature. You could have also disproven this point directly in the introduction. The TS (as a mathematical construct) is a 0-dimensional point and hitting it would require an atomic geometry with infinite precision, which is not possible.

Results

The graph for the endothermic direction of the F-H-H reaction looks almost like a step function. This is an unanticipated result to me and I would have liked to see a comment from you. When calculating the TS energy, you do actually know what the energy of the TS is. The potential energy of the atomic configurations is independent of how you got to them, so the potential energy in the perfectly symmetrical TS calculation can be used, even though it would never go on to react. You may also be able to get a better estimate of the reactant potential energy by fitting the potential energy curve with an analytical function and then taking the limit of time approaching infinity.--Bg1512 (talk) 15:09, 11 May 2017 (BST)