Raman-induced vibrational coherence control of bond-selective HOD photodissociation with two UV pulses.

Selective bond cleavage in polyatomic molecules remains a key challenge in chemical physics and femtochemistry because vibrational energy rapidly redistributes, hindering targeted bond activation. Here, we theoretically show that two ultraviolet pulses enable mode-selective photodissociation in HOD, which has distinct O-H and O-D bonds. The first pulse initiates dissociation and, through resonant Raman scattering, creates vibrational coherence in the ground electronic state. The second pulse, applied after a controlled delay, interacts with this coherence to determine which bond breaks. By adjusting the inter-pulse delay, we tune the H + OD-to-D + OH branching ratio from above 2.0 (single-pulse) to about 1.3. Modifying the chirps of both pulses further reduces the ratio to nearly 1.0. These results show that vibrational coherence from resonant Raman scattering can be used to control chemical reactions on femtosecond timescales, and this method may be applicable to other molecular systems.