Direct observation of bimolecular reactions of ultracold KRb molecules

M.-G. Hu (1, 2, 3) , Y. Liu (1, 2, 3) , D. Grimes (1, 2, 3) , Y.-W. Lin (1, 2, 3) , A. Gheorghe (2) , R. Vexiau (4) , N. Bouloufa-Maafa (4) , O. Dulieu (4) , T. Rosenband (2) , K.-K. Ni (1, 2, 3)

1 Department of Chemistry and Chemical Biology, Harvard University, Cambridge, MA 02138
2 Department of Physics [Harvard University]
3 Harvard-MIT Center for Ultracold Atoms
4 LAC - Laboratoire Aimé Cotton

Femtochemistry techniques have been instrumental in accessing the short time scales necessary to probe transient intermediates in chemical reactions. Here we take the contrasting approach of prolonging the lifetime of an intermediate by preparing reactant molecules in their lowest ro-vibronic quantum state at ultralow temperatures, thereby drastically reducing the number of exit channels accessible upon their mutual collision. Using ionization spectroscopy and velocity-map imaging of a trapped gas of potassium-rubidium molecules at a temperature of 500~nK, we directly observe reactants, intermediates, and products of the reaction 4040^{40}K8787^{87}Rb + 4040^{40}K8787^{87}Rb →→\rightarrow K22_2Rb∗22∗^*_2 →→\rightarrow K22_2 + Rb22_2. Beyond observation of a long-lived energy-rich intermediate complex, this technique opens the door to further studies of quantum-state resolved reaction dynamics in the ultracold regime.

Domaines: Physique Quantique [quant-ph]

M.-G. Hu, Y. Liu, D. Grimes, Y.-W. Lin, A. Gheorghe, et al.. Direct observation of bimolecular reactions of ultracold KRb molecules. Science, 2019, 366 (6469), pp.1111-1115. ⟨10.1126/science.aay9531⟩. ⟨hal-03007592⟩