Hello everyone We have tried PEC calculation on some polyatomic molecules using MOLPRO/CASSCF. Each PECs contains 3 lines for neutral ground, anionic ground, and anionic excited state. By just looking at the PECs, we have noticed some peaks in the anionic curve in all molecules, around after Req (equilibrium distance of that bond). So, my confusion is that, why and what causes these peaks and what is the significance of peaks in PEC curves? For reference, I'm attaching some of the PECs.
Thanks in advance.
Were these curves calculated by just enlarging one distance or were the other coordinates open for relaxation? In the first case, you might simply have used a trajectory which didn't follow the minimum with respect to the non-reactive coordinates.
In the second case, one option coming to my mind is that you have encountered a repulsive Coulomb barrier situation. I don't know any literature on bond dissociation, but in photoelectron spectroscopy of multiply charged molecular/complex anions these also play a role in detaching electrons from the molecules. The basic idea is that in order to leave the molecule, the negative charge of the leaving entity has to pass by the other negative charges which constitute the repulsive Coulomb barrier. For photoelectrons, here is a publication of my former colleagues:
Article Resonant tunneling through the repulsive Coulomb barrier of ...
The physics may be somewhat different for dissociation, but you could generate electron density contour plots and check if you see something odd happening around your maxima.
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