Valence orbital response to conformers of n-butane

Abstract

Individual outer valence orbital responses to rotations of the C–C central bond of butane (C4H10) are explored on the torsional potential energy surface. Orbital ionization energies, topologies and momentum distributions for the four most significant butane conformation are presented, as snapshots of the conformational variations. The analysis is based on quantum mechanically generated information from coordinate space and momentum space, a technique called dual space analysis (DSA). By comparison with experimental measurements of photo-electron spectra (PES) for energies and of electron momentum spectra (EMS) for energies and Dyson orbitals, we demonstrate that the individual outer valence orbitals of these conformers response differently to the rotations of the central C–C bond of n-butane. Orbital signatures of other higher energy conformations, such as orbitals la 2 and 5a 1 of conformation D (C2v ), are identified. This finding indicates a co-existence of butane conformations, although the global minimum structure of anti-butane, A (C2h ), is dominant. Orbital topology and electron charges redistribution during the transformation provide useful information on the chemical bonding and related chemical reactions.