Generalized electronic diabatic approach to structural similarity and the Hammond postulate

Abstract

ABSTRACT:We revisit the notion of structural similarity along a reaction path within the context of a generalized electronic diabatic (GED) molecular model. In this approach, a reaction involving two closed-shell stable species is described as the evolution of a quantum state that superimposes at least three diabatic electronic species (reactant, product, and an open-shell transition state) coupled by an external electromagnetic field. Reactant and product amplitudes in this general state are also modulated by changing the geometry of a system of classical positive charges interacting with the electrons. By mapping these amplitudes over nuclear configurational space, we can follow the total quantum state along a reaction coordinate and establish its similarity to each of the diabatic species. As a result, chemical processes, and useful notions such as those of energy barriers and the Hammond postulate, emerge as consequence of Franck-Condon-like transitions between quantum states.

Constructing quantum mechanical models starting from diabatic schemes: Quantum states for simulations bond break/formation—I. Feshbach-like quantum states and electronuclear wave functions

“…It results in the construction of electrons-nuclei separation via a procedure based on quantum numbers [1] that departs from the mechanical one followed in the BO model [23]; the path followed and potentialities are illustrated with the help of refs. [2][3][4][5][6][7][8][9] and references therein. Here, for the sake of completeness, an overview with fresh ideas is presented.…”

“…Now we move on from abstract quantum analyses to contact with more traditional manners to describe chemical processes yet keeping the quantum flavor. So far we have done this with analytical semi-classic situations [4][5][6][7][8][9].…”

“…[1][2][3][4][5][6][7][8][9]20] exact basis states f k,g(k) (q, ξ ) can be the place for further modeling. For example, we consider here mappings introducing electronuclear separation by quantum numbers [1]:…”

“…The development of diabatic schemes serving as a ground to formulate a quantum theory of chemical reactions has been one of our continued focus of interest [1][2][3][4][5][6][7][8][9]. Besides, quantum technology at laboratory level is producing important progress [10][11][12][13][14][15][16][17] and, as a result, the way we quantum chemists look at simple chemical systems has begun to be turned upside down.…”

“…The system is simple enough to allow illustrating the main aspects of quantum states underlying the phenomena. Here, the wheeling concept requires quantum physics of systems coupled to external probing sources; this is in contrast the traditional PESs [23] (see also [2][3][4][5][6][7][8][9]) that play now a subsidiary (yet illustrative) role via diabatic procedures. Section 2 situates the problem; it starts from the notion that molecular (coherent) quantum states, expressed as linear superpositions over basis states.…”