Bonding Description of the Harpoon Mechanism

TL;DR

This paper investigates the electron transfer processes in diatomic molecules to distinguish the harpoon mechanism from regular bonding, proposing new descriptors and analysis methods for bond formation.

Contribution

It introduces a novel approach to identify the harpoon mechanism using electron transfer variation points, electron sharing indices, and electron localization functions.

Findings

Maximal electron transfer occurs at half transfer in all studied mechanisms.

The harpoon mechanism's avoided crossing coincides with the maximal electron transfer point.

Electron sharing indices and localization functions effectively distinguish bonding mechanisms.

Abstract

The lowest-lying states of LiH have been widely used to develop and calibrate many different methods in quantum mechanics. In this paper we show that the electron-transfer processes occurring in these two states are a difficult test for chemical bonding descriptors and can be used to assess new bonding descriptors on its ability to recognize the harpoon mechanism. To this aim, we study the bond formation mechanism in a series of diatomic molecules. In all studied electron-reorganization mechanisms, the maximal electron-transfer variation point along the bond formation path occurs when about half electron has been transferred from one atom to another. If the process takes places through a harpoon mechanism, this point of the reaction path coincides with the avoided crossing. The electron sharing indices and one-dimensional plots of the electron localization function and the Laplacian of the electron density along the molecular axis can be used to monitor the bond formation in diatomics and provide a distinction between the harpoon mechanism and a regular electron-reorganization process.