Influencing Strong Field Excitation Dynamics through Molecular Structure

Abstract

We report the loss of discrete above-threshold ionization photoelectron peaks in the strong-field (800 nm, 60 fs, 3.6 - 9.0 10 13 W‚cm -2 ) excitation in a series of polyatomic molecules of increasing characteristic length. The molecules, biphenyl (C12H10), diphenylmethane (C13H12), and diphenylethane (C14H14), have two phenyl groups spaced by a bridge of zero, one, or two carbon atoms. The photoelectron spectra correlate with the characteristic lengths, not the number of atoms, of these molecules. The molecules having the smallest and largest numbers of atoms (but similar characteristic lengths) display a broad featureless distribution of photoelectron kinetic energies, peaked at lower kinetic energies and extending to many tens of electronvolts. Diphenylmethane, the molecule with intermediate number of atoms but the smallest characteristic length, displays a photoelectron spectrum containing discrete peaks in this range of laser intensities. The absence of discrete photoelectron peaks in the spectra of biphenyl and diphenylethane is interpreted using an eigenstate lifetime model based on calculated field ionization rates in an intense laser field. Finally, the abundance of photoelectrons with high kinetic energies suggests higher probability of electron rescattering in the polyatomic molecules in comparison with atomic intense field ionization.