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Prior studies of halobenzene−ammonia complexes have shown that the nature of the cationic intermediate (i.e., Wheland-type vs ion-radical) may play a key role in determining the reaction products. To probe this link, we report here the reaction dynamics of the chlorobenzene-ammonia 1:1 complex (PhCl···NH3) using product ion imaging following two-color resonant two-photon ionization. A threshold value of 8.863 ± 0.008 eV was determined for the appearance of protonated aniline, which accompanies Cl atom loss and is the dominant product channel at energies near threshold. Scanning down to energies close to threshold, we find no evidence for a roaming halogen radical mechanism leading to HCl products, which was evidenced in the related bromobenzene−ammonia complex, and proceeded through an ion-radical intermediate structure. Here, supporting calculations indicate that both types of intermediates are present, but the Wheland-type structure is significantly more stable. Addressing a key question of earlier work, analysis of the PhCl···NH3 potential energy surface (PES) in the reactant region establishes a complicated entrance channel pathway linking the in-plane σ-type complex to the Wheland intermediate (iWH) on the [PhCl···NH3]+• cationic surface. This pathway involves stepwise transition of the weakly bound ammonia from the initial in-plane σ-type complex to an ortho Wheland intermediate, followed by rearrangement to the ipso position. Finally, given that fluorine has been shown to stabilize aromatic ions, we hypothesized that fluorine substitution might alter the structure of the intermediate, favoring the ion-radical intermediate. To test this hypothesis, as an illustrative example the PES of the meta-PhClF-NH3 system on the cationic surface was computed. Confirming our hypothesis, these calculations show an inversion in stability for the Wheland-type and ion−radical complex intermediates, with the latter preferred energetically at the examined level of theory. 

A single photoexcited electron−hole pair within a polar semiconductor nanocrystal (SNC) alters the charge screening and shielding within it. Perturbations of the crystal lattice and of the valence and conduction bands result, and the quantum-confinement states in a SNC shift uniquely with a dependence on the states occupied by the carriers. This shifting is termed quantum-state renormalization (QSR). This Perspective highlights QSR in semiconductor quantum wires and dots identified in time-resolved transient absorption and two-dimensional electronic spectroscopy experiments. Beyond the interest in understanding the principles of QSR and energy-coupling mechanisms, we pose the contributions of QSR in time-resolved spectroscopy data must be accounted for to accurately identify the time scales for intraband relaxation of the carriers within SNCs.