Rotational Quenching of CO by collision with H$_2$

Collisions of CO with H$_2$ have been the subject of numerous experimental and theoretical investigations, due in part, to their high abundance in a wide range of astronomical environments. We present quantum mechanical scattering calculations for the rotational relaxation of CO in collisions with para- and ortho-H$_2$ using the quantum close-coupling and coupled states approaches. State-to-state cross sections for the pure rotational quenching of the $j$=1, 2, $\cdots$, 10 levels of CO were computed using the new H$_2$-CO potential surface of Jankowski and Szalewicz (JS, 2005). The results are compared to previous calculations and to cross sections obtained with the 1998 potential of JS. Rate coefficients for astrophysically relevant temperatures, as well as in the ultracold regime, are also obtained. We acknowledge support from NASA grant NNG04GM59G.