title: Strong field ionization to multiple electronic states in water.
abstract: High harmonic spectra show that laser-induced strong field ionization of water has a significant contribution from an inner-valence orbital. Our experiment uses the ratio of H(2)O and D(2)O high harmonic yields to isolate the characteristic nuclear motion of the molecular ionic states. The nuclear motion initiated via ionization of the highest occupied molecular orbital (HOMO) is small and is expected to lead to similar harmonic yields for the two isotopes. In contrast, ionization of the second least bound orbital (HOMO-1) exhibits itself via a strong bending motion which creates a significant isotope effect. We elaborate on this interpretation by solving the time-dependent Schrödinger equation to simulate strong field ionization and high harmonic generation from the water isotopes. We expect that this isotope marking scheme for probing excited ionic states in strong field processes can be generalized to other molecules.
authors.affiliation: Stanford PULSE Institute, SLAC National Accelerator Lab, 2575 Sand Hill Road, Menlo Park California 94025, USA.
authors.forename: Joseph P
authors.initials: JP
authors.lastname: Farrell
authors.forename: Simon
authors.initials: S
authors.lastname: Petretti
authors.forename: Johann
authors.initials: J
authors.lastname: Förster
authors.forename: Brian K
authors.initials: BK
authors.lastname: McFarland
authors.forename: Limor S
authors.initials: LS
authors.lastname: Spector
authors.forename: Yulian V
authors.initials: YV
authors.lastname: Vanne
authors.forename: Piero
authors.initials: P
authors.lastname: Decleva
authors.forename: Philip H
authors.initials: PH
authors.lastname: Bucksbaum
authors.forename: Alejandro
authors.initials: A
authors.lastname: Saenz
authors.forename: Markus
authors.initials: M
authors.lastname: Gühr