Adiabatic quantum trajectory capture method for cold and ultra-cold chemical reactions
Résumé
While direct reactions with activation barriers are now routinely calculated, reactions going through a longlived
intermediate complex are much more difficult to study[1, 2]. Complex-forming reactions are often barrierless
and are thus relevant to the field of cold and utra-cold chemistry [2]. With decreasing temperature, wave effects
become increasingly important and may dominate the collisional behavior at ultralow temperatures. Capture theories
(close-coupling expansion with boundary conditions applied in the reactant channel) are often used to study
complex-forming reactions [3, 4].
The Langevin capture model is often used to describe barrierless reactive collisions. At very low temperature,
quantum effects may alter this simple capture image and dramatically affect the reaction probability. In this talk,
we use the trajectory-ensemble reformulation of quantum mechanics without wavefunctions recently proposed by
Poirier and coworkers[5, 6] to compute adiabatic-channel capture probabilities and cross-sections for the reaction
Li + CaH(v = 0; j = 0)!LiH + Ca at low and ultra-low temperatures. The captured quantum trajectory takes full
account of tunneling and quantum reflection along the radial collision coordinate. Our approach turns out to be
very fast and accurate, down to extremely low temperatures.