Mode-selective H ₂ O dissociation on Pt(111) under two-dimensional confinement

Understanding how spatial confinement alters chemical reactivity at surfaces remains an unanswered but fundamental question. In this work, we investigate the dissociative chemisorption of H₂O on Pt(111), focusing on how two-dimensional (2D) confinement, introduced by graphene (Gr), boron nitride (BN), and graphitic carbon nitride (C₃N₄), modulates the mode-selectivity of this reaction. Building on our earlier findings of barrier reduction under such confinements, we employ a reaction path Hamiltonian approach to uncover how vibrational energy redistribution is affected in both vibrationally adiabatic and non-adiabatic regimes. Our findings reveal that 2D confinement significantly enhances dissociation probabilities for both ground state and vibrationally excited state. Remarkably, the ground-state reactivity under confinement reaches levels comparable to those achieved <i>via</i> single-quantum vibrational excitation of H₂O on the bare surface. The symmetric stretching and bending modes have more influence on reactivity owing to their greater softening near the transition state. Non-adiabatic factors mediated by curvature- and Coriolis-couplings influence energy redistribution by amplifying low-energy reactivity. In the unconfined case, Coriolis interactions dominate and facilitate over-the-barrier processes through vibrational de-excitation. Among the confined cases, Gr cover exhibits the highest effect on reactivity, yielding nearly barrierless dissociation pathways through strong coupling between the reaction path and vibrationally excited symmetric and bending modes. Altogether, the analysis of spatial confinement and vibrational excitation in this work paves the way for rational catalytic design.