Collisional cooling of polar diatomics in He-3 and He-4 buffer gas: A quantum calculation at ultralow energies

The anisotropic interactions of three polar molecules-CO, HF, and LiH-with He atoms (in their ground electronic states), obtained from accurate ab initio calculations that explicitly include their vibration-to-translation coupling terms are analyzed in detail, to compare their relative features. The q uantum scattering calculations of their rotovibrational inelastic cross sections are conducted using a recently proposed multichannel treatment, the modifi ed variable phase method, that has been implemented by the authors and applied here to ultralow collision energies. A comparison of the different relaxatio n efficiencies exhibited by the three title molecules in releasing their internal vibrational energy during ultracold collisions with He-4 and He-3 buffer gas is performed in detail and specific suggestions for experimental choices are extracted from these findings.