title: Probing proton dynamics in molecules on an attosecond time scale.
abstract: We demonstrate a technique that uses high-order harmonic generation in molecules to probe nuclear dynamics and structural rearrangement on a subfemtosecond time scale. The chirped nature of the electron wavepacket produced by laser ionization in a strong field gives rise to a similar chirp in the photons emitted upon electron-ion recombination. Use of this chirp in the emitted light allows information about nuclear dynamics to be gained with 100-attosecond temporal resolution, from excitation by an 8-femtosecond pulse, in a single laser shot. Measurements on molecular hydrogen and deuterium agreed well with calculations of ultrafast nuclear dynamics in the H2+ molecule, confirming the validity of the method. We then measured harmonic spectra from CH4 and CD4 to demonstrate a few-femtosecond time scale for the onset of proton rearrangement in methane upon ionization.
authors.affiliation: Blackett Laboratory, Imperial College London, Prince Consort Road, South Kensington, London SW7 2BZ, UK.
authors.forename: S
authors.initials: S
authors.lastname: Baker
authors.forename: J S
authors.initials: JS
authors.lastname: Robinson
authors.forename: C A
authors.initials: CA
authors.lastname: Haworth
authors.forename: H
authors.initials: H
authors.lastname: Teng
authors.forename: R A
authors.initials: RA
authors.lastname: Smith
authors.forename: C C
authors.initials: CC
authors.lastname: Chirila
authors.forename: M
authors.initials: M
authors.lastname: Lein
authors.forename: J W G
authors.initials: JW
authors.lastname: Tisch
authors.forename: J P
authors.initials: JP
authors.lastname: Marangos