Vibrational relaxation of vibrationally and rotationally excited CO molecules by He atoms

This work presents a detailed quantum mechanical study of rovibrationally inelastic He+CO collisions in a wide range of translational and internal energies of the collision partners. Fully converged coupled states calculations of rate constants for vibrational relaxation of CO(v=1) by He are found to be in excellent agreement with experimental measurements at temperatures between 35 and 1500 K. The role of rotational energy for vibrational relaxation of CO is investigated and it is illustrated that the CO molecules in the first excited vibrational state can exhibit near-resonant vibrational relaxation when they are initially in high rotational excitation and the collision energy is small. A reduced channel coupled states approach neglecting low vibrational states in the basis set is implemented for calculations of rate constants for vibrational and rotational energy transfer in collisions of vibrationally excited CO molecules with He atoms. It is shown that initial vibrational excitation significantly increases rate constants for vibrationally inelastic collisions but does not affect purely rotational energy transfer. (C) 2002 American Institute of Physics.