Quantum nature of molecular vibrational quenching: Water - molecular
  hydrogen collisions
  Rates of conversions of molecular internal energy to and from kinetic energy
by means of molecular collision allows to compute collisional line shapes and
transport properties of gases. Knowledge of ro-vibrational quenching rates is
necessary to connect spectral observations to physical properties of warm
astrophysical gasses, including exo-atmospheres. For a system of paramount
importance in this context, the vibrational bending mode quenching of H2O by
H2, we show here that exchange of vibrational to rotational and kinetic energy
remains a quantum process, despite the large numbers of quantum levels involved
and the large vibrational energy transfer. The excitation of the quantized
rotor of the projectile is by far the most effective ro-vibrational quenching
path of water. To do so, we use a fully quantum first principle computation,
potential and dynamics, converging it at all stages, in a full coupled channel
formalisms. We present here rates for the quenching of the first bendingmode of
ortho-H2O by ortho H2, up to 500K, in a fully converged coupled channels
formalism.
