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Publication Metadata only Exploring a dynamical path for C2H− and NCO− formation in dark molecular clouds(Springer, 2016) Iskandarov, Ibrokhim; Gianturco, Francesco Antonio; Carelli, Fabio; Wester, Roland; Department of Chemistry; Yurtsever, İsmail Ersin; Faculty Member; Department of Chemistry; College of Sciences; 7129This paper deals with the possible formation of two molecular anions often considered likely components in the physical environments of the interstellar medium (ISM): C2H- and NCO-. They are both discussed here by computationally following the radiative association (RA) mechanism starting from C-2(-), H, NC- and O as partners. The corresponding RA total cross sections produced by the calculations are in turn employed to generate the overall association rates over the relevant range of temperatures. The latter are found to be in line with other molecular ions formed by RA but not large enough to uniquivocally suggest this path as the main route to the anions formation in the ISM. Other possible paths of formation are also analysed and discussed. The presence of resonant structures during the association dynamics for both systems is found by the calculations and their consequences are discussed in some detail in the present study.Publication Metadata only Narrow escape problem in synaptic molecular communications(Association for Computing Machinery, Inc, 2022) Koca, Çağlar; Department of Electrical and Electronics Engineering; N/A; Akan, Özgür Barış; Civaş, Meltem; Faculty Member; PhD Student; Department of Electrical and Electronics Engineering; College of Engineering; Graduate School of Sciences and Engineering; 6647; N/AThe narrow escape problem (NEP) is a well-known problem with many applications in cellular biology. It is especially important to understand synaptic molecular communications. Active regions of synapses, also known as apposition zones, are connected to synaptic cleft through narrow slits, from which neurotransmitters can escape to or return from the cleft into the apposition zones. While neurotransmitters leakage into the cleft might be desired for the reuptake process, escaping neurotransmitters might trigger an undesired, i.e., false-positive or action potential in the post-synaptic terminal. Obtaining analytic solutions to NEPs is very challenging due to its geometry dependency. Slight alterations in either or both shape or the size of the hole and the outer volume may cause drastic changes in the solution. Thus, we need a simulation-based approach to solve NEPs. However, NEP also requires the size of the hole to be much smaller than the dimensions of the volume. Combined with the requirement for Brownian motion, where the step size is much smaller than the dimensions of the volume, simulations can be prohibitively long, even for modern computers. Therefore, in this work, we suggest a simulation algorithm that simultaneously satisfies the NEP and Brownian motion simulation requirements. Our simulation framework can be used to quantify the neurotransmitter leakage within synaptic clefts.Publication Metadata only Non-monotonic size effects on the structure and thermodynamics of coulomb clusters in three-dimensional harmonic traps(Springer, 2007) Calvo, Florent; Department of Chemistry; Yurtsever, İsmail Ersin; Faculty Member; Department of Chemistry; College of Sciences; 7129Finite-size effects on the static and thermodynamical properties of small three-dimensional clusters of identical charged particles confined by an harmonic trap are investigated using global optimization and numerical simulations. The relative stabilities of clusters containing up to 100 particles are estimated from the second energy derivatives, as well as from the energy gap between the two lowest-energy structures at a given size. We also provide a lower bound for the number of permutationally independent minima, as a function of size, up to n=75. Molecular dynamics and exchange Monte Carlo simulations are performed to get insight into the finite temperature behaviour of these clusters. By focusing on specific sizes, we illustrate the interplay between the stable structures, the possible competition between different isomers, and the melting point. In particular, we find that the orientational melting phenomenon known in two-dimensional clusters has an equivalent form in some three-dimensional clusters. The vibrational spectra, computed for all sizes up to 100, shows an increasing number of low-frequency modes, but comparing to hydrodynamical theory reveals strong correlation effects. Finally, we investigate the effects of the trap anisotropy on the general shape of Coulomb clusters, and on the melting point of a selected case.Publication Metadata only Quenching efficiency of "hot" polar molecules by he buffer gas at ultralow energies: quantum results for MgH and LiH rotations(Springer, 2008) Gonzalez Sanchez, Lola; Bodo, Enrico; Gianturco, Franco A.; Department of Chemistry; Yurtsever, İsmail Ersin; Faculty Member; Department of Chemistry; College of Sciences; 7129Rotationally superelastic collisions are computed from quantum dynamical calculations for the two title systems, down to the very low collision energies of interest in cold trap experiments. The results are obtained via ab initio interaction potentials, the one for the MgH-He system being given here for the first time and discussed in details in the present paper. The calculations show marked differences in behaviour for both cooling efficiency rates at vanishing temperatures and individual cross sections between levels, and their origin is related to target structural properties and with specific features of the two potentials.Publication Metadata only Quenching vibrations of cesium dimers by He at low and ultralow temperatures: quantum dynamical calculations(Springer, 2011) Caruso, D.; Tacconi, M.; Bovino, S.; Gianturco, F. A.; Department of Chemistry; Yurtsever, İsmail Ersin; Faculty Member; Department of Chemistry; College of Sciences; 7129This paper analyses in detail the energy redistribution from the upper vibrational levels of Cs dimers, thought to be obtained from initial recombination processes that generate excited internal states of the triplet configuration (3) I pound (u) (+) . Their quenching is examined as they are made to further collide with (4)He buffer gas at temperatures below and around 100 mK. The relevant cross sections are computed by using a multichannel quantum dynamical approach and employ a full, ab initio potential energy surface. Due to their smallness (see Ref. [R.B. Ross, J.M. Powers, T. Atashroo, W.C. Ermler, I.A. LaJohn, P. Christiansen, J. Chem. Phys. 93, 6654 (1999)]) the fine structure effects have not been explicitly included in this study. The final, cumulative cross-sections are discussed and analyzed in terms of the overall quenching behavior shown by different initial states of the dimer and in terms of the changing ratios between collisional cooling and vibrational quenching cross sections as a function of trap temperature. The corresponding quenching rates are also computed and analysed.Publication Metadata only Solvation of K+ in helium droplets(Springer, 2007) Yıldırım, Erol; Yurtsever, Mine; Bodo, Enrico; Gianturco, Franco A.; Department of Chemistry; Yurtsever, İsmail Ersin; Faculty Member; Department of Chemistry; College of Sciences; 7129Solvation of K+ in helium droplets is studied by classical simulation methods. We have previously shown that additive potentials can be used to describe structures of helium droplets when an ionic species is present. Here, we present an accurate ab-initio potential for the K+ - He interaction. Global minima of KHen+ for up to n=70 are searched for employing Basin Hopping Monte Carlo simulations with a random growth scheme. The extent of the solvation is analyzed. A clear formation of two shells with 15 and 23 atoms is detected.