Full-dimensional vibrational quenching of CO in collisions with H$_2$

We report a six-dimensional (6D) potential energy surface (PES) for the CO-H$_2$ collision system calculated using the explicitly correlated coupled-cluster (CCSD(T)-F12B) method as implemented in MOLPRO2010.1 and fitted using an invariant polynomial method. In the fit of the 6D PES, the total polynomial expansion power was restricted to 6 and expansion coefficients were obtained using standard weighted least-squares optimization for potential energies up to 10,000 cm$^{-1}$. Close-coupling scattering calculations have been performed on the new 6D PES for rotational and vibrational quenching of CO in collisions with H$_2$ using the TwoBC code. Cross sections for $j=0 \rightarrow 1$ pure rotational transition in CO, convoluted with a Gaussian kinetic energy distribution, show better agreement with measurement than that obtained on a recently available 4D PES. State-to-state and total quenching cross sections and rate coefficients for the vibrational quenching in CO($v_1=1, j_1=0$)+H$_2$($v_2=0, j_2=0$) $\rightarrow$ CO($v_1^{\prime}=0, j_1^{\prime}$)+H$_2$($v_2^{\prime}=0, j_2^{\prime}=0$) collisions, for $j_1^{\prime}=0, 1, \cdots, 25$ are presented and compared with experimental results and previous calculations using 4D and 5D PESs and various decoupling approximati