Determination of intramolecular isotope effects in the Be+(2P3/2) + HD reaction.

Isotope effects in the Be+(2P3/2) + HD reaction were investigated using an integrated ion trap and high-resolution time-of-flight mass spectrometer at a collision energy of 285 K (Ecoll/kB). The total rate constant was measured to be (1.4 ± 0.1) × 10-9 cm3/s, consistent with predictions from classical capture theory. The branching ratio of BeD+ + H to BeH+ + D was determined for the first time and found to be 3.7 ± 0.6, indicating a significant isotope effect. Comparisons with the pairwise energy model and phase space theory suggest that the reaction does not proceed through a purely abstraction or insertion mechanism. Time-dependent quantum dynamics calculations further underscore the importance of accurately describing short-range interactions to reproduce the observed branching behavior. These results establish a well-characterized benchmark system for studying isotope effects and reaction mechanisms in ion-molecule collisions under quantum-state control.