Imaging vibrationally mediated photodissociation dynamics of MgCl

Magnesium monochloride (MgCl), a reactive intermediate in high-temperature combustion and plasma chemistry, has been theoretically recognized as a promising candidate for laser cooling. However, its key molecular parameters-such as bond dissociation energy, vibrational frequency, and excited-state topography-remain unclear due to inconsistencies between experimental and theoretical results. Here, we directly observe the photodissociation of MgCl molecules in the coupled electronically excited 42Σ+ and 52Σ+ states via developing laser-ablation molecular beam and time sliced ion velocity imaging techniques. By analyzing the vibrationally state-resolved velocity of recoiling magnesium atoms from the photolysis of MgCl at 193 nm, we determined a bond dissociation energy of 29 464(110) cm-1 and a vibrational frequency of 435(61) cm-1 for MgCl(X2Σ+). The measured dissociation energy serves as a lower bound for D0 and is notably higher than prior reported data, indicating that vibrational excitation effectively reduces the energy required for bond dissociation-a plausible reason for the underestimations observed in earlier measurements. Insights into the dissociation energy and dissociation dynamics of MgCl provide a key experimental basis for advancing theoretical models of reactive intermediates and prospective applications in laser cooling.