The evolution of the monoelectron dihydrogen bond H ⋯e⋯ H in the symmetric and asymmetric cluster anions ( FH ) n {e}( HF ) m J. Chem. Phys. 118, 10939 (2003) In this article, we have presented ultrafast charge transfer dynamics through halogen bonds following vertical ionization of representative halogen bonded clusters. Subsequent hole directed reactivity of the radical cations of halogen bonded clusters is also discussed. Furthermore, we have examined effect of the halogen bond strength on the electron-electron correlation-and relaxation-driven charge migration in halogen bonded complexes. For this study, we have selected A-Cl (A represents F, OH, CN, NH 2 , CF 3 , and COOH substituents) molecules paired with NH 3 (referred as ACl:NH 3 complex): these complexes exhibit halogen bonds. To the best of our knowledge, this is the first report on purely electron correlation-and relaxation-driven ultrafast (attosecond) charge migration dynamics through halogen bonds. Both density functional theory and complete active space self-consistent field theory with 6-31+G(d, p) basis set are employed for this work. Upon vertical ionization of NCCl· · ·NH 3 complex, the hole is predicted to migrate from the NH 3 -end to the ClCN-end of the NCCl· · ·NH 3 complex in approximately 0.5 fs on the D 0 cationic surface. This hole migration leads to structural rearrangement of the halogen bonded complex, yielding hydrogen bonding interaction stronger than the halogen bonding interaction on the same cationic surface.

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Ices of acetylene (C2H2) and ammonia (NH3) were irradiated with energetic electrons to simulate interstellar ices processed by galactic cosmic rays in order to investigate the formation of C2H3N isomers. Supported by quantum chemical calculations, experiments detected product molecules as they sublime from the ices using photoionization reflectron time‐of‐flight mass spectrometry (PI‐ReTOF‐MS). Isotopically‐labeled ices confirmed the C2H3N assignments while photon energies of 8.81 eV, 9.80 eV, and 10.49 eV were utilized to discriminate isomers based on their known ionization energies. Results indicate the formation of ethynamine (HCCNH2) and 2H‐azirine (c‐H2CCHN) in the irradiated C2H2:NH3 ices, and the energetics of their formation mechanisms are discussed. These findings suggest that these two isomers can form in interstellar ices and, upon sublimation during the hot core phase, could be detected using radio astronomy.

In general, charge migration can occur via pure electron-electron correlation and relaxation or via coupling with nuclear motion. We must understand both aspects of charge migration through the non-hydrogen noncovalent bonds to harness full potential of the halogen-, chalcogen-, pnicogen- and tetrel-bonded photosensitive functional materials. This feature article, however, is focused on the pure relaxation- and correlation-driven charge migration, subsequent charge localization, and finally on charge-directed reactivity in the non-hydrogen noncovalent bonded clusters. Pure relaxation- and correlation-driven charge migration can occur on a several hundred attosecond (as) time scale, and this is why chemical dynamics associated with this pure electronic charge migration can be named "attochemistry". One of the efficient ways to elucidate the attochemistry is via the vertical ionization by monitoring a nonstationary electronic charge density that evolves in time while the nuclear configuration remains unchanged. So far, attochemistry of several halogen-, chalcogen-, pnicogen-, and tetrel-bonded clusters has been studied theoretically by our group. All the interesting predictions have been summarized in this Feature Article. The time scales of relaxation- and correlation-driven charge migration through the halogen, chalcogen, pnicogen, and tetrel noncovalent bonds are found to be quite similar (approximately in the range of 300-600 as) in different (1:1) AX:NH and AX:OH complexes (where A represents different substituents, such as NH, CN, etc.). Basis sets do not exhibit any effect on the predicted charge migration time scale. A very long intermolecular distance (approximately more than 10 Å), for which (physically) no noncovalent bonding interaction can be present, ceases the intermolecular charge migration. The strength of the electron-electron correlation interaction influences the charge migration through these noncovalent bonds, making charge migration faster with a higher correlation interaction. The initial nuclear configuration affects the charge migration through the non-hydrogen noncovalent bonds. For large clusters, in which both hydrogen and non-hydrogen noncovalent bonds are formed, non-hydrogen noncovalent bonds are found to facilitate the charge migration preferentially over the hydrogen bonds. As a result of nuclear wavepacket delocalization, the attosecond charge oscillation in noncovalent bonded clusters decoheres. This renders charge localization. Subsequent charge-directed reactivity is discussed. This article is the first review on the attochemistry of non-hydrogen noncovalent bonded clusters.

The electron-electron relaxation and correlation-driven charge migration process, which features pure electronic aspect of ultrafast charge migration phenomenon, occurs on a very short timescale in ionized molecules and molecular clusters, prior to the onset of nuclear motion. In this article, we have presented nature of ultrafast pure electronic charge migration dynamics through Cl ..... N, Cl ..... O, Br ..... N, and Br ..... O halogen bonds, explored using density functional theory. We have explored the role of donor, acceptor, electron correlation, vibration and rotation in charge migration dynamics through these halogen bonds. For this work, we have selected ClF, Cl 2 , ClOH, ClCN, BrF, BrCl, BrOH, and BrCN molecules paired with either NH 3 or H 2 O. We have found that the timescale for pure electron-electron relaxation and correlation-driven charge migration through the Cl ..... N, Br ..... N, Cl ..... O, and Br ..... O halogen bonds falls in the range of 300-600 attosecond. The primary driving force behind the attosecond charge migration through the Cl ..... N, Br ..... N, Cl ..... O, and Br ..... O halogen bonds is the energy difference (E) between two stationary cationic orbitals (LUMO-β and HOMOβ), which together represents the initial hole density immediately following vertical ionization. We have also predicted that the strength of electron correlation has significant effect on the charge migration timescale in Cl ..... N, Br ..... N, Cl ..... O, and Br ..... O halogen bonded clusters. Vibration and rotation are also found to exhibit profound effect on attosecond charge migration dynamics through halogen bonds.