  Accurate rate coefficients for molecular vibrational transitions due to
collisions with H$_2$, critical for interpreting infrared astronomical
observations, are lacking for most molecules. Quantum calculations are the
primary source of such data, but reliable values that consider all internal
degrees of freedom of the collision complex have only been reported for
H$_2$-H$_2$ due to the difficulty of the computations. Here we present
essentially exact full-dimensional dynamics computations for rovibrational
quenching of CO due to H$_2$ impact. Using a high-level six-dimensional
potential surface, time-independent scattering calculations, within a full
angular-momentum-coupling formulation, were performed for the deexcitation of
vibrationally excited CO. Agreement with experimentally-determined results
confirms the accuracy of the potential and scattering computations,
representing the largest of such calculations performed to date. This
investigation advances computational quantum dynamics studies representing
initial steps toward obtaining CO-H$_2$ rovibrational quenching data needed for
astrophysical modeling.
