Non-adiabatic dissociation dynamics of Ar• • •I2 (E, v) intermolecular vibrational levels probed using velocity-map imaging

Ion time-of-flight velocity-map imaging was used to measure the kinetic-energy distributions of the I-2 ion-pair fragments formed after photoexcitation of Ar center dot center dot center dot I-2 complexes to intermolecular vibrational levels bound within the Ar + I-2 (E, vE = 0-2) potential energy surfaces. The kinetic-energy distributions of the I-2 products indicate that complexes in the Ar center dot center dot center dot I-2 (E, vE) levels preferentially dissociate into I-2 in the D and ss ion-pair states with no change in I-2 vibrational excitation. The energetics of the levels prepared suggest that there is a non-adiabatic coupling of the initially prepared levels with the continuum of states lying above the Ar + I-2 (D, vD = vE) and Ar + I-2 (ss, v ss = vE) dissociation limits. The angular anisotropies of the I-2 product signals collected for many of the Ar center dot center dot center dot I-2 (E, vE) levels have maxima parallel to the laser polarization axis. This contradicts expectations for the prompt dissociation of complexes with T-shaped geometries, which would result in images with maxima perpendicular to the polarization axis. These anisotropies suggest that there is a perturbation of the transition moment in these clusters or there are additional intermolecular interactions, likely those sampled while traversing above the attractive wells of the lower-energy potentials during dissociation. I-2 (D', vD') products are also identified when preparing several of the low-lying levels localized in the T-shaped well of the Ar + I-2 (E, vE = 0-2) potentials, and they are formed in multiple.D' vibrational levels spanning energy ranges up to 500 cm(-1). Published under an exclusive license by AIP Publishing. https://doi.org/10.1063/5.0166512