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 (C 12 H 10 ), diphenylmethane (C 13 H 12 ), and diphenylethane (C 14 H 14 ), 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.

Closing the Loop on Bond Selective Chemistry Using Tailored Strong Field Laser Pulses

“…This dynamic shifting of energy levels implies that there will be transient field-induced resonances (or Freeman resonances) water, benzene, and naphthalene . The oscillatory nature of the intense laser excitation also leads to above threshold ionization (ATI) peaks in the photoelectron spectrum .…”

“…55 Evidence for these resonances in the case of molecules has been obtained by measuring the strong field photoelectron spectroscopy of a number of molecules including acetone, acetylene, 52 water, benzene, and naphthalene. 56 The oscillatory nature of the intense laser excitation also leads to above threshold ionization (ATI) peaks in the photoelectron spectrum. 5 These are denoted by peaks spaced by the photon energy extending to many photons above the minimum number required for ionization.…”

“…Evidence for the broadening of eigenstates during the strong field excitation process can be found in the photoelectron measurements for acetylene, 50 benzene, and naphthalene. 56 In each of these molecules the photoelectron spectra contain a welldefined series of features that can be assigned using the method of FIRE MPI as described previously. As the laser intensity increases above that required for detection of photoelectrons, the features begin to broaden.…”

Method for estimating the influence of an external electric field on the probability of photochemical transformations

“…This effect manifests itself for photochemical reactions with a high density of quanta of the initiating radiation and for the application of a static field with a significant potential. Numerous investigations [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15] have addressed this question. Additional possibilities for controlling the process in order to prepare new compounds are appearing.…”

Molecules and clusters in strong laser fields

“…This dynamic shifting of energy levels implies that there will be transient field-induced resonances (or Freeman resonances) [66]. Evidence for these resonances in the case of molecules has been obtained by measuring the strong field photoelectron spectroscopy of a number of molecules including acetone, acetylene [63], water, benzene and naphthalene [67]. The oscillatory nature of the intense laser excitation also leads to above threshold ionization (ATI) peaks in the photoelectron spectrum [2].…”