Ultrafast formation dynamics of D₃⁺ from the light-driven bimolecular reaction of the D₂-D₂ dimer

The light-driven formation of trihydrogen cation has been attracting considerable attention because of its important role as an initiator of chemical reactions in interstellar clouds. To understand the formation dynamics, most previous studies focused on creating H₃⁺ or D₃⁺ from unimolecular reactions of various organic molecules. Here we observe and characterize the ultrafast formation dynamics of D₃⁺ from a bimolecular reaction, using pump-probe experiments that employ ultrashort laser pulses to probe its formation from a D₂-D₂ dimer. Our molecular dynamics simulations provide an intuitive representation of the reaction dynamics, which agree well with the experimental observation. We also show that the emission direction of D₃⁺ can be controlled using a tailored two-colour femtosecond laser field. The underlying control mechanism is in line with what is known from the light control of electron localization in the bond breaking of single molecules.