CONICET | Buscador de Institutos y Recursos Humanos

In September 1999 a news announced in the front page of Nature shocked the chemical and the physical communities: atomic orbitals had been observed and imaged for the first time. Immediately, the debate began. On one side, some authors considered the correspondence between experimental images and textbooks diagrams as an empirical confirmation of theoretical predictions. On the other side, different arguments were directed to conclude that the experiments were misinterpreted: orbitals cannot be observed because they do not exist. In this work we take that event as a starting point for rethinking the ontological status of the chemical world, a problem we have discussed in previous works. Here we address the issue of the relationship between molecular chemistry and quantum mechanics from an ontological viewpoint and in the light of the concept of orbital. In particular, we consider two kinds of arguments proposed for denying the existence of orbitals. We reject the first kind, based on the fact that the Schrödinger equation cannot be analytically solved in many-electron atoms. The analysis of the second kind of arguments allows us to stress the deep breakdown between the quantum concept of wavefunction and the concept of orbital as used in molecular chemistry. On this basis, we argue that the conclusion about the non-referring character of the term orbital relies on an ontological reductionism that leads to hardly acceptable consequences when sustained in a non-contradictory way. Our final purpose is to show that these consequences can be avoided from an ontological pluralism according to which orbitals, even if non-existent in the quantum ontology, are real entities in the ontological realm of molecular chemistry. From this perspective, atomic orbitals can be observed, in the same sense as the multiplicity of entities non-reducible to quantum mechanics are observed in the effective practice of the many branches of science.

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