Strong fields induce ultrafast rearrangement of H-atoms in H$_2$O

TL;DR

This study demonstrates that strong optical fields can induce ultrafast rearrangement of hydrogen atoms in water molecules within a single 10 fs laser pulse, challenging previous assumptions about molecular ionization and fragmentation.

Contribution

It provides the first evidence of ultrafast H-atom rearrangement in H₂O under strong fields, with detailed quantum-chemical insights into the process.

Findings

H-atoms in H₂O form H₂⁺ within 10 fs under strong fields.

Thresholds for field strength and duration necessary for rearrangement are established.

Quantum calculations identify the molecular state and geometry during rearrangement.

Abstract

H-atoms in H$_2$O are rearranged by strong optical fields generated by intense, 10 fs laser pulses to form H$_2^+$, against prevailing wisdom that strong fields inevitably lead to multiple molecular ionization and the subsequent Coulomb explosion into fragments. This atomic rearrangement is shown to occur within a single 10 fs pulse. Comparison with results obtained with $\sim$300-attosecond long strong fields generated using fast Si$^{8+}$ ions helps establish thresholds for field strength and time required for such rearrangements. Quantum-chemical calculations reveal that H$_2^+$ originates in the $^1$A state of H$_2$O$^{2+}$ when the O-H bond elongates to 1.15 a.u. and the H-O-H angle becomes 120$^o$. Bond formation on the ultrafast timescale of molecular vibrations (10 fs for H$_2^+$) has hitherto not been reported.