1,014 research outputs found

    Characterization Of Charge Accommodation In Biologically Important Hydrogen-Bonded Clusters

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    The underlying motivation of chemical physics and physical chemistry is to understand naturally occurring chemical and physical processes from the nanoscopic molecular level to the macroscopic condensed phase. Over the past half-century, experimentalists have developed a number of laser-based analytical techniques to bridge the gap between the bulk phase and the single molecule. Here, we look at bulk phase and gas phase clusters to compare the local hydrogen-bonded network. To better understand the role noncovalent interactions have on biologically relevant building blocks in a natural environment, we compare the microhydration of gas phase cluster ions to condensed phase spectra. The accommodation of excess charge plays an essential character in a number of biochemical processes involving peptides, nucleobases, aerosols, etc. A time-of-flight mass spectrometer was constructed to isolate discrete numbers of solute and solvent molecules for spectroscopic interrogation via light-matter interactions. We also employed high-resolution Raman spectroscopy for vibrational interrogation of temperature dependence in crystalline lattice modes as well as effects of surface-enhanced Plasresonances. Electronic structure methods were employed for accurate spectral assignment and identification of structural motifs

    Structures and Stabilities of Carbon Chain Clusters Influenced by Atomic Antimony

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    The C-C bond lengths of the linear magnetic neutral CnSb, CnSb+ cations and CnSb− anions are within 1.255–1.336 Å, which is typical for cumulene structures with moderately strong double-bonds. In this report, we found that the adiabatic ionization energy (IE) of CnSb decreased with n. When comparing the IE~n relationship of CnSb with that of pure Cn, we found that the latter exhibited a stair-step pattern (n ≄ 6), but the IE~n relationship of CnSb chains took the shape of a flat curve. The IEs of CnSb were lower than those of corresponding pure carbon chains. Different from pure carbon chains, the adiabatic electron affinity of CnSb does not exhibit a parity effect. There is an even-odd alternation for the incremental binding energies of the open chain CnSb (for n = 1–16) and CnSb+ (n = 1–10, when n > 10, the incremental binding energies of odd (n) chain of CnSb+ are larger than adjacent clusters). The difference in the incremental binding energies between the even and odd chains of both CnSb and pure Cn diminishes with the increase in n. The incremental binding energies for CnSb- anions do not exhibit a parity effect. For carbon chain clusters, the most favorable binding site of atomic antimony is the terminal carbon of the carbon cluster because the terminal carbon with a large spin density bonds in an unsaturated way. The C-Sb bond is a double bond with Wiberg bond index (WBI) between 1.41 and 2.13, which is obviously stronger for a carbon chain cluster with odd-number carbon atoms. The WBI of all C-C bonds was determined to be between 1.63 and 2.01, indicating the cumulene character of the carbon chain. Generally, the alteration of WBI and, in particular, the carbon chain cluster is consistent with the bond length alteration. However, the shorter C-C distance did not indicate a larger WBI. Rather than relying on the empirical comparison of bond distance, the WBI is a meaningful quantitative indicator for predicting the bonding strength in the carbon chain

    A Themed Issue of Functional Molecule-based Magnets: Dedicated to Professor Masahiro Yamashita on the Occasion of his 65th Birthday

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    Research on molecule-based magnetic materials was systematized in the 1980s and expanded rapidly. A Special Issue focusing on molecule-based magnetic substances was published in Magnetochemistry. However, the functionalities of the substances increase daily; therefore, the researchers’ quest is not yet in decline. Research on molecule-based magnetism developed across many fields, including chemistry, physics, material chemistry, and applied physics, and the use of the various functionalities of these molecule-based magnetic substances has greatly influenced research on spin-based devices. In honor of Professor Masahiro Yamashita, who contributed greatly to this field, I have put together a Special Issue that highlights ten groundbreaking articles. The issue is entitled, “A Themed Issue of Functional Molecule-Based Magnets: Dedicated to Professor Masahiro Yamashita on the Occasion of his 65th Birthday”. I wish to thank the authors for their dedicated work, and the referees and editorial staff for the time they invested commenting on the articles

    An experimental study of the reactivity of CN- and C3N- anions with cyanoacetylene (HC3N)

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    International audienceThe reactions of the CN- and C3N- anions with cyanoacetylene HC3N, of special interest for the chemistry of Titan’s upper atmosphere, have been investigated by means of FTICR mass-spectrometry. Primary ions, CN- and C3N-, have been produced by dissociative electron attachment (DEA) from BrCN and BrC3N, and prepared in a clean way before reaction. Total rate constants have been measured for both reactions at 300 K and are found to be: (3.9 ± 0.5) 10-9 and (1.0 ± 0.2) 10-10 cm3.s-1 for the reaction of HC3N with CN- and C3N-, respectively. For the CN- + HC3N reaction, proton transfer is found to be the only reactive channel within our detection limits. Proton transfer is also dominant for the C3N- + HC3N reaction but the resulting ionic product being identical to the primary ion C3N-, this process is transparent for the kinetics of the C3N- + HC3N reaction and the kinetic rate retrieved corresponds to a slow and competitive detachment pathway. Yet the nature and energetics of the neutral product(s) formed through this process remain unknown. Additional experiments using isotopic products have allowed to retrieve specific rate constants associated to the proton transfer channel in the C315N- + HC3N and C3N- + HC315N reactions and the measured rates are found to be significantly lower than for the CN- + HC3N system. This decrease and the evolution of reactivity when going from CN- to C3N- and the opening of a new detachment pathway is finally discusse

    Electronic States of Fullerene Anions and Endohedral Fullerenes

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    In recent years, fullerenes, as rising stars in carbon clusters, have been widely applied in various fields of science and technology. The high electron affinity of fullerenes, due to unique geometric and electronic structures, leads to wide applications in many fields, e.g., organic solar cells, supercapacitors, catalyzers, and superconductive materials. Due to the difficulty to synthesize of carbon clusters and to determine their structures experimentally, researchers have paid much attention to the theoretical studies of their geometric and electronic structures. It is only recently that it became possible to apply state-of-the-art theoretical methods, e.g., equation of motion coupled cluster singles and doubles method for electron affinities (EA-EOM-CCSD) to these large molecular systems. With such high cost methods, the full picture of electronic states of the first known fullerene C60 has finally been revealed. Study of electronic structures of large molecular systems, such as fullerenes, has become a great challenge for modern theoretical and computational chemistry. This thesis is devoted to the theoretical study of the electronic states of fullerene anions (e.g., C20–) and fullerene derivatives, utilizing accurate approaches. The latter includes endohedral fullerenes (e.g., Li@C20 and Li@C60) and carbon rings (e.g., C20). To the best of our knowledge, our work is the first study on bound states of the C20– fullerene anion, employing accurate theoretical approaches. We find that the smallest fullerene anion C20–, can form one superatomic and a manifold of valence bound states. It indicates that possessing superatomic bound states is one of the common properties of fullerenes. We hope that this finding sheds light on the study of fullerenes applications in the future. Our theoretically estimated adiabatic electron affinity of the C20– fullerene, is consistent with the electron affinity obtained in the photoelectron experiment. It verifies the validity of the application of high accurate EA-EOM-CCSD method in studying electronic structures of fullerenes. The endohedral fullerenes, e.g., Li@C20 and Li@C60, have attracted great attention due to their enhanced properties compared to the parent fullerenes. Our research on Li@C20 shows that the smallest fullerene, i.e., C20, can steal valence electron from the guest Li atom and form a charge separated donor-acceptor system. The Coulomb effect of Li+ is to stabilize the bound states, both valence and superatomic. Noteworthy, due to their different nature, the stabilizing effect on valence states is stronger than on superatomic states. The extra electron density distribution of superatomic states of the charge separated endohedral system is more compact compared to that of the parent fullerene, while the distribution of valence states does not exhibit this behavior. Based on our calculations on Li@C60, we have found several excited states. Most of the electronic states are charge separated states, the appearance of Li+ stabilized the excited states of Li@C60 compared to those of the parent isolated anion without changing their characters, similarly to our finding for Li@C20. Importantly, for Li@C60 we reported a hitherto unknown non-charge-separated state, which we referred to as the caged-electron state. This state is neither a valence nor a superatomic state, since its extra charge density is mostly distributed at the center of the cage. We demonstrate that the caged-electron state is formed due to the large radius of the C60 cage, which reduces the Coulomb attraction effect between Li+ and the negative carbon cage of the endohedral fullerene. In much larger fullerenes, e.g., Li@C180, this state even becomes the ground state, due to the much weaker Coulomb attraction effect. It is a great example of the impact of the fullerene’s size on its electronic structures. Additionally, we have mentioned several possible applications of this new kind of state. Last but not least, we turn to the carbon ring as the isomer of fullerenes. Carbon rings are intriguing and elegant species, but determining their geometry is an ongoing challenge. We have performed geometry optimization, vibrational frequency calculations and potential energy surface scans, based on EA-EOM-CCSD. Our work reveals that, similar to its fullerene isomer, the C20– ring can possess several bound states, including one superatomic state. Moreover, our calculation shows a symmetry breaking of the C20– ring anion structure occurring upon attaching an electron to the neutral ring. The discussion of the possible symmetry breaking mechanisms indicates that the shrinking and distortion of the ring upon electron attachment leading to the symmetry breaking, is a result of the interplay between the symmetry breaking and the totally symmetric modes. The discussion enriches the palette of possible symmetry breaking phenomena in carbon clusters

    Predicting the Stability of Fullerene Allotropes Throughout the Periodic Table

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    We present a systematic, first-principles study of the role of elemental identity in determining electronic, energetic, and geometric properties of representative A₂₈B₂₈, A₃₀B₃₀, and A₃₆B₃₆ III–V (A = B, Al, Ga, or In and B = N, P, or As) and II–VI (A = Zn or Cd and B = S or Se) fullerene allotropes. A simple descriptor comprising electronegativity differences and covalent radii captures the relative fullerene stability with respect to a nanoparticle reference, and we demonstrate transferability to group IV A₇₂ (A = C, Si, or Ge) fullerenes. We identify the source of relative stability of the four- and six-membered-ring-containing A₃₆B₃₆ and A₂₈B₂₈ fullerene allotropes to the less stable, five-membered-ring-containing A₃₀B₃₀ allotrope. Relative energies of hydrogen-passivated single ring models explain why the even-membered ring structures are typically more stable than the A₃₀B₃₀ fullerene, despite analogies to the well-known C₆₀ allotrope. The ring strain penalty in the four-membered ring is comparable to or smaller than the nonpolar bond penalty in five-membered rings for some materials, and, more importantly, five-membered rings are more numerous in A₃₀B₃₀ than four-membered rings in A₃₆B₃₆ or A₂₈B₂₈ allotropes. Overall, we demonstrate a path forward for predicting the relative stability of fullerene allotropes and isomers of arbitrary shape, size, and elemental composition.National Science Foundation (U.S.) (ECCS-1449291

    THEORETICAL STUDIES OF DIPOLE-BOUND ANIONS AND SMALL WATER CLUSTERS

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    Part I of this work deals with dipole-bound anions of moderately and highly polar molecules. High level electronic structure calculations are performed on nitrile, carbonate, and sulfite containing molecules. The results are compared against experimental data obtained from Rydberg electron transfer, photoelectron spectroscopy, and field detachment studies. Explanations to the unusual trends in the electron binding energies of the series of nitrile containing molecules are suggested. Calculation results also help in suggesting an explanation to the interesting dissociative electron attachment observed in ethylene sulfite. Part II of the thesis is devoted to theoretical studies of neutral and anionic water clusters. Neutral water clusters are important in establishing the bridge between a single water molecule and its bulk phase, while still allowing for accurate quantum mechanical calculations. Anionic water clusters on the other hand, are valuable species in the study of electron capture, solvation, and transfer, which are important chemical and biological processes. Here, we focus mainly on the energetic and spectroscopic features of water clusters. Namely, we consider the effects of anharmonicity and high-level electron correlation to the vibrational frequencies and to the binding energies of the (H2O)n, n = 2-6 neutral clusters. We also attempt to assign the vibrational spectrum of the (H2O)7-Arm cluster, which shows unusual complexity and Ar solvation dependence, when compared with smaller clusters

    Poster Session

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    Posters presented by: P01: Adam S. Abbott, University of Georgia P02: Yasmeen Abdo, University of Mississippi P03: Vibin Abraham, Virginia Tech P04: Asim Alenaizan, Georgia Institute of Technology P05: Isuru R. Ariyanthna, Auburn University P06: Brandon W. Bakr, Georgia Institute of Technology P07: [Matthew Bassett, Georgia Southern University] P08: Alexandre P. Bazanté, University of Florida P09: Andrea N. Becker, University of Tennessee P10: Randi Beil, University of Tennessee P11: Andrea N. Bootsma, University of Georgia/Texas A&M University P12: Adam Bruner, Louisiana State University P13: Lori A. Burns, Georgia Institute of Technology P14: Chanxi Cai, Emory University P15: Katherine A. Charbonnet, University of Memphis P16: Marjory C. Clement, Virginia Tech P17: Wallace D. Derricotte, Emory University P18: Harkiran Dhah, University of Tennessee P19: Manuel Díaz-Tinoco, Auburn University P20: Vivek Dixit: Mississippi State University P21: Eric Van Dornshuld, Mississippi State University P22: Katelyn M. Dreux, University of Mississippi P23: Narendra Nath Dutta, Auburn University P24: William Earwood, University of Mississippi P25: Thomas L. Ellington, University of Mississippi P26: Marissa L. Estep, University of Georgia P27: Yanfei Guan, Texas A&M University P28: Andrew M. James, Virginia Tech P29: Yifan Jin, University of Florida P30: Dwayne John, Middle Tennessee State University P31: Sarah N. Johnson, University of Mississippi P32: Noor Md Shahriar Khan, Auburn University P33: Monika Kodrycka, Auburn University P34: Ashutosh Kumar, Virginia Tech P35: Elliot Lakner, University of Alabama P36: Robert W. Lamb, Mississippi State University P37: S. Paul Lee, University of Mississippi P38: Zachary Lee, University of Alabama P39: Conrad D. Lewis, Middle Tennessee State University P40: Guangchao Liang, Mississippi State University P41: Chenyang Li, Emory University P42: Hannah C. Lozano, University of Memphis P43: SharathChandra Mallojjala, University of Georgia/Texas A&M University P44: Zheng Ma, Duke University P45: Elvis Maradzike, Florida State University P46: Ashley S. McNeill, University of Alabama P47: Stephen R. Miller, University of Georgia P48: W. J. Morgan, University of Georgia P49: Apurba Nandi, Emory University P50: Daniel R. Nascimento, Florida State University P51: Brooke N. Nash, Mississippi College P52: Carlie M. Novak, Georgia Southern University P53: Young Choon Park, University of Florida P54: Kirk C. Pearce, Virginia Tech P55: Rudradatt (Randy) Persaud, University of Alabama P56: Karl Pierce, Virginia Tech P57: Kimberley N. Poland, University of Mississippi P58: Chen Qu, Emory University P59: Duminda S. Ranasinghe, University of Florida P60: Hailey B. Reed, University of Mississippi P61: Matthew Schieber, Georgia Institute of Technology P62: Jeffrey B. Schriber, Emory University P63: Thomas Sexton, University of Mississippi P64: Holden T. Smith, Louisiana State University P65: Aubrey Smyly, Mississippi College P66: B. T. Soto, University of Georgia P67: Trent H. Stein, University of Alabama P68: Cody J. Stephan, Georgia Southern University P69: Thomas Summers, University of Memphis P70: Zhi Sun, University of Georgia P71: Monica Vasiliu, University of Alabama P72: Jonathan M. Waldrop, Auburn University P73: Tommy Walls, Southern Louisiana University P74: Qingfeng (Kee) Wang, Emory University P75: Constance E. Warden, Georgia Institute of Technology P76: Jared D. Weidman, University of Georgia P77: Melody Williams, University of Memphis P78: Donna Xia, University of Alabama P79: Qi Yu, Emory University P80: Boyi Zhang, University of Georgia P81: Tianyuan Zhang, Emory University P82: Michael Zott, Georgia Institute of Technolog
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