Mapping of orbital structure from high harmonic generation through the molecular dipole moment

Abstract

Here we examine the connection between high order harmonic generation (HHG) and molecular electronic structure within the strong field approximation (SFA) by surveying the dipole moment between the highest occupied molecular orbital (HOMO) and a plane wave approximation to the continuum state. We take as examples a number of wavefunctions in a Gaussian basis corresponding to hydrogen 1s, and the 2s and 2p x orbitals that are the building blocks for the N2, CO2 and other molecular orbitals. The harmonic dipole moment amplitude and phase is examined as a function of angle between a fixed axis in the frame of the wave function and the continuum electron momentum vector. We then examine, and discuss, the results for a number of molecules where experimental data already exists such as N2, CO2, acetylene and allene with orbitals calculated within a Gaussian basis using the GAMESS program. Concrete predictions can be obtained from this procedure against which measurements can be compared. In this way the validity of ideas for structural imaging of molecules via HHG or via XUV photoionization can be tested.