Chemical Bonding in Hydrogen Molecular Ion and Competition between Laser‐induced Ionization and Dissociation

Abstract

AbstractJust as a helium atom is a prototype for atoms, a hydrogen molecular ion is a prototype for chemical bonding in molecules. In the presence of an external field, the latter also serves as a prototype for which field‐induced ionization and dissociation compete with each other. Pauli was the first to examine the nature of chemical bonding in terms of the old quantum theory. In view of the recent developments of nonlinear dynamics and quantum chaos, we re‐examine the negative conclusion that he reached in his thesis. In particular, we are interested in finding out whether the classical three‐body system is stable and whether any part of the chemical bonding can be attributed to its classical stability. Our result shows that indeed classical phase space structures exist which contribute to chemical bonding, when quantized semiclassically. Thus chemical bonding is not a purely quantum phenomenon, as generally believed.We also examine the classical dynamical behavior of this three‐body system in the presence of an external field beyond the Born‐Oppenheimer approximation. Interesting competition exists between ionization, dissociation, and Coulomb explosion. Although ionization dominates over dissociation at high laser fields, there exists a range of laser intensity below 150 TW/cm2 for which we can concentrate on dissociation alone without significant interference from the ionization process.