Sub-femtosecond quantum dynamics of the strong-field ionization of water to the 2B1 and Ã2A1 states of the cation

Abstract

Motivated by recent efforts to achieve sub-femtosecond structural resolution in various molecular systems, we have performed a femtosecond quantum dynamics study of the water cation in the ²B₁ and òA₁ electronic states. Autocorrelation functions for H₂O⁺ and D₂O⁺ are calculated for such electronic states by solving numerically the time-dependent Schrödinger equation. From the ratio of the squared autocorrelation functions of D₂O⁺ and H₂O⁺, the high-order harmonic generation signals are calculated. Substantial vibrational dynamics is found in the òA₁ state as compared to the one in ²B₁, which supports recent experimental findings of Farrell et al., Phys. Rev. Lett., 2011, 107, 083001. Maxima in the above ratio are also predicted at ∼1.1 fs and ∼1.6 fs for the ²B₁ and òA₁ states, respectively. The expectation values of the positions of the atoms in H₂O⁺ as a function of time reveal a strong excitation of the bending mode in the òA₁ state, which explains the observed vibrational dynamics. The peaks in the ratios of the squared autocorrelation functions are also explained in terms of the evolving geometries of the water cation.