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A full nine-dimensional potential-energy surface for hydrogen molecule-water collisions
Alexandre Faure1, Pierre Valiron, Michael Wernli
1Laboratoire d'Astrophysique, Unité Mixte de Recherche 5571, Centre National de la Recherche Scientifique, Université Joseph Fourier, B.P. 53, 38041 Grenoble cedex 09, France. alexandre.faure@obs.ujf-grenoble.fr
The Journal of Chemical Physics
|June 25, 2005
Summary
We developed a new model for hydrogen (H2) and water (H2O) molecule interactions. This model accurately predicts vibrational relaxation rates, impacting our understanding of cosmic water emission.
Area of Science:
- Astrophysics and Physical Chemistry
- Computational Chemistry
Background:
- Water (H2O) and hydrogen (H2) molecules are abundant in the universe.
- Their interactions are crucial for understanding astronomical phenomena like water masers and line emission in star-forming regions.
Purpose of the Study:
- To compute a comprehensive nine-dimensional potential energy surface for the H2O-H2 system.
- To calculate state-to-state rotational and vibrational energy transfer rate constants for H2O-H2 collisions.
Main Methods:
- High-accuracy, explicitly correlated wave function calculations were used to derive the interaction potential.
- Quasiclassical trajectory (QCT) calculations were employed to determine state-to-state rate constants for vibrational relaxation.
Main Results:
- A full nine-dimensional potential energy surface for H2O-H2 was generated.
- Vibrational relaxation rate constants for the H2O (upsilon2) bending mode were computed for temperatures ranging from 500 K to 4000 K.
- Calculated high-temperature rates are consistent with experimental data and significantly larger than previously published values.
Conclusions:
- The new H2O-H2 potential energy surface provides an accurate description of intermolecular interactions.
- The computed vibrational relaxation rates challenge existing astrophysical models and necessitate a re-evaluation of space-borne water emission spectra.
- The methodology is transferable to other astrophysically relevant molecular systems.