Rotational quenching of C2 with 3He and 4He collisions at ultracold temperatures

Quantum mechanical closed coupling scattering calculations are carried out at temperatures ranging from 10(-8) K to 100 K for studying rotational transitions of C-2 due to collisions with He-3 and He-4 employing our new C-2-He potential energy surface computed at the CCSD(T)-F12b/aug-cc-pVQZ level of theory. Among the isotopes of He, the heavier He-4 isotope has larger value of rotational quenching cross section than 3He isotope. Wigner's threshold law holds below 10(-1) cm(-1). Quenching rate coefficients suggest that C-2 can be cooled with He-4 buffer gas. The dominance of He-4 on C-2 molecule is further addressed by calculating the predissociation lifetime of C-2.

Automated summary

In this study, quantum mechanical closed coupling scattering calculations are performed to investigate rotational transitions of C-2 due to collisions with He-3 and He-4. A new C-2-He potential energy surface computed at the CCSD(T)-F12b/aug-cc-pVQZ level of theory is utilized. The results show that the heavier He-4 isotope has a larger rotational quenching cross section compared to the 3He isotope. Wigner's threshold law is observed below 10(-1) cm(-1). The findings suggest that C-2 can be cooled by collisions with He-4 buffer gas.