Recent Publications

Jorge Kohanoff

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  1. Title: Dynamics of Excess Electronic Charge in Aliphatic Ionic Liquids Containing the Bis(trifluoromethylsulfonyl)amide Anion

    Author(s): Xu C., Durumeric A., Kashyap H.K., Kohanoff J.J., Margulis C.J.

    Journal of the American Chemical Society, 135, No. 46, pp. 17528-17536 (October 24 2013)

    doi: 10.1021/ja409338z
    Abstract



    In a recent article (J. Am. Chem. Soc. 2011, 133, 20186) we investigated the initial spatial distribution of dry excess electrons in a series of room-temperature ionic liquids (RTILs). Perhaps unexpectedly, we found that in some alkylammonium-based systems the excess negative charge resided on anions and not on the positive cations. Following on these results, in the current paper we describe the time evolution of an excess electronic charge introduced in alkylammonium- and pyrrolidinium-based ionic liquids coupled with the bis(trifluoromethylsulfonyl)amide ([Tf2N–]) anion. We find that on a 50 fs time scale an initially delocalized excess electron localizes on a single [Tf2N–] anion which begins a fragmentation process. Low-energy transitions have a very different physical origin on the several femtoseconds time scale when compared to what occurs on the picosecond time scale. At time zero, these are intraband transitions of the excess electron. However after 40 fs when the excess electronic charge localizes on a single anion, these transitions disappear, and the spectrum is dominated by electron-transfer transitions between the fragments of the doubly charged breaking anion.

  2. Title: Electronic stopping power of H and He in Al and LiF from first principles

    Author(s): Zeb M.A., Kohanoff J., Sanchez-Portal D., Artacho E.

    Nuclear Instruments & Methods in Physics, Research Section B - Beam Interactions with Materials and Atoms, 303, pp. 59-61 (May 15 2013)

    doi: 10.1016/j.nimb.2012.12.022
    Abstract



    Non-linearities in the electronic stopping power of light projectiles in bulk Al and LiF are addressed from first principles using time-evolving time-dependent density functional theory. In the case of Al, the agreement of the calculations with experiments for H and He projectiles is fair, but a recently observed transition for He from one value of the electronic friction coefficient to a higher value at v similar to 0.3 a.u. is not reproduced by the calculations. For LiF, better accuracy is obtained as compared with previously published simulations, albeit the threshold remains overestimated.

  3. Title: Organic Synthesis in the Interstellar Medium by Low-Energy Carbon Irradiation

    Author(s): McBride E.J., Millar T.J., Kohanoff J.J.

    Journal of Physical Chemistry A, 117, No. 39, pp. 9666-9672 (10 May 2013)

    doi: 10.1021/jp312342v
    Abstract



    We present a first principles molecular dynamics (FPMD) study of the interaction of low-energy neutral carbon projectiles with amorphous solid water clusters at 30 K. Reactions involving the carbon atom at an initial energy of 11 and 1.7 eV with 30-molecule clusters have been investigated. Simulations indicate that the formation of hydroxymethylene, an intermediate in formaldehyde production, dominates at the higher energy. The reaction proceeds by fragmenting a water molecule, binding the carbon to the OH radical, and saturating the C valence with a hydrogen atom that can arise from the originally dissociated water molecule, or through a chain of proton transfer events. We identified several possible pathways for the formation of HCOH. When the initial collision occurs at the periphery of the cluster, we observe the formation of CO and the evaporation of water molecules. At the lower energy water fragmentation is not favorable, thus leading to the formation of weakly bound carbon-water complexes.