Strong field ionization to multiple electronic states in water

Area of Science:

• Quantum dynamics
• Atomic and molecular physics
• Laser-matter interactions

Background:

• Strong field ionization of molecules is a key process in understanding electron dynamics.
• High harmonic generation (HHG) is a sensitive probe of molecular electronic structure and dynamics.
• Isotopic substitution can provide unique insights into molecular processes.

Purpose of the Study:

• To investigate the contribution of inner-valence orbitals to laser-induced strong field ionization of water.
• To differentiate nuclear dynamics initiated from different molecular orbitals using isotopic labeling.
• To simulate and interpret experimental observations of high harmonic spectra from water isotopes.

Main Methods:

• Experimental measurement of high harmonic spectra from H2O and D2O.
• Analysis of the ratio of high harmonic yields between H2O and D2O.
• Theoretical simulations using the time-dependent Schrödinger equation.

Main Results:

• Strong field ionization of water involves significant contributions from an inner-valence orbital.
• Ionization of the highest occupied molecular orbital (HOMO) leads to minimal isotope effects.
• Ionization of the second least bound orbital (HOMO-1) induces a pronounced bending motion, creating a significant isotope effect.
• Simulations confirm the experimental observations and the role of nuclear motion.

Conclusions:

• The study successfully uses an isotope marking scheme to probe excited ionic states in strong field processes.
• Distinct nuclear motions are initiated depending on the ionized molecular orbital.
• The methodology is expected to be applicable to other molecules for studying their electronic and nuclear dynamics.