Quasiresonant energy transfer in ultracold atom-diatom collisions

Quantum and classical quasiresonant vibration-rotation energy transfer is investigated for ultracold He-H₂ collisions. Classical trajectory computations show that extremely strong correlations between Δj and Δv persist at low energies, though the changes themselves are less than one quantum. Quantum computations show that quasiresonant transitions occur in the limit of zero collision energy but that threshold effects become important and that some quasiresonant channels close. The qualitative similarity between classical and quantum results suggests that they share a common mechanism.