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.

光驱动的三氢阳离子的形成因其作为星际云中化学反应引发剂的重要作用而引起了相当大的关注。为了了解形成动力学，大多数先前的研究集中于从各种有机分子的单分子反应中产生H ₃ ⁺或D ₃ ^{+ 。}在这里，我们通过泵浦探针实验观察并表征了双分子反应中D ₃ ⁺的超快形成动力学，该实验采用超短激光脉冲来探测 D ₂ –D ₂二聚体的形成。我们的分子动力学模拟提供了反应动力学的直观表示，这与实验观察非常吻合。我们还表明，可以使用定制的双色飞秒激光场来控制D ₃ ⁺的发射方向。基本的控制机制与单分子键断裂中电子局域化的光控制已知的一致。