Vibrational-state and isotope dependence of high-order harmonic generation in water molecules

We report calculations on high-order harmonic generation in water molecules. Spectra are determined for various initial vibrational states of H2O and its isotope D2O. It is demonstrated that the ratio of the spectra for D2O and H2O is close to unity when the initial state is the vibronic ground state, indicating that nuclear dynamics is of minor importance. For vibrationally excited initial states, the high-harmonic intensities show a clear dependence on both the initial-state quantum number and the isotopic species. © 2010 The American Physical Society.