Papers by Sivaram Arepalli
Evidence for tunneling in the reaction O(3P)+HD
Chemical Physics Letters, Mar 1, 1987
... PHYSICS LETTERS 20 March 1987 EVIDENCE FOR TUNNELING IN THE REACTION 0(3P)+HD Daniel C. ROBIE... more ... PHYSICS LETTERS 20 March 1987 EVIDENCE FOR TUNNELING IN THE REACTION 0(3P)+HD Daniel C. ROBIE, Sivaram ... 581 Volume 134, number 6 CHEMICAL PHYSICS LETTERS 20 March 1987 [7] JM Bowman, AF Wagner, SP Walch and TH Dunning Jr.,J. Chem ...
Detection of Cl atoms and HCl molecules by resonantly enhanced multiphoton ionization
Chemical Physics Letters, Jul 1, 1985
Volume 118, number 1 CHEMICAL PHYSICS LETTERS 12 July 1985 DETECTION OF Cl ATOMS AND HO MOLECULES... more Volume 118, number 1 CHEMICAL PHYSICS LETTERS 12 July 1985 DETECTION OF Cl ATOMS AND HO MOLECULES BY RESONANTLY ENHANCED MULTIPHOTON IONIZATION Sivarain AREPALLI, Nathan PRESSER, Daniel ROBIE and Robert J. GORDON Department of ...
ChemInform Abstract: Ab initio Predictions and Experimental Confirmation of Large Tunneling Contributions to Rate Constants and Kinetic Isotope Effects for Hydrogen Atom Transfer Reactions
Chemischer Informationsdienst, Sep 30, 1986
Resonantly enhanced two‐photon spectroscopy of HCl and DCl in the 77 000–87 000 cm<sup>−</sup><sup>1</sup> region
Journal of Chemical Physics, May 15, 1987
The two-photon spectra of HCl and DCl were studied using the technique of resonantly enhanced mul... more The two-photon spectra of HCl and DCl were studied using the technique of resonantly enhanced multiphoton ionization. Rovibrational bands were observed for the X 1Σ+→V 1Σ+, E 1Σ+, F 1Δ2, d 3Π1, f 3Δ2, and g 3Σ− transitions. The results are compared with the single photon spectra of Ginter, Douglas, and co-workers and with the molecular orbital calculations of Bettendorf et al.
The rate constant for the reaction O(<sup>3</sup><i>P</i>)+D<sub>2</sub> at low temperatures
Journal of Chemical Physics, 1989
The rate constant for the reaction of O(3P)+D2 was measured over the temperature range 343 to 446... more The rate constant for the reaction of O(3P)+D2 was measured over the temperature range 343 to 446 K using the laser photolysis–resonance fluorescence technique. The results can be fit well with a two-parameter Arrhenius function and are in excellent agreement with the previous measurements of Presser and Gordon and with the recent high temperature measurements of Michael. The data are also in very good agreement with the theoretical calculations of Joseph et al. and of Bowman et al. and demonstrate that tunneling makes a significant contribution to the rate coefficient over the entire range of temperatures studied in this experiment. The Arrhenius behavior of the rate constant supports the conclusions of Robie et al. in their study of the intramolecular isotope effect in O(3P)+HD, where it was found that tunneling plays a major role at low temperatures.
Single-photon VUV laser-induced fluorescence spectrum of HCl
Nucleation and Atmospheric Aerosols, 1989
One-photon and multiphoton spectroscopy of HCI and HBr
In recent years, there has been renewed interest in the study of hydrogen halides, especially hyd... more In recent years, there has been renewed interest in the study of hydrogen halides, especially hydrogen chloride and hydrogen bromide. The simplicity of HCl and HBr makes them amenable for computation, and they are of interest to theoreticians carrying out light-heavy-light molecular reactions. The role of HCl is very poorly understood in the semiconductor etching process and is under study at different laboratories.
Nanotechnology, Feb 26, 2004
We explore Raman microprobe capabilities of visualizing single-wall carbon nanotubes (SWCNTs). Al... more We explore Raman microprobe capabilities of visualizing single-wall carbon nanotubes (SWCNTs). Although this technique is limited to the micron scale, we demon trate that images of individual SWCNTs, bundles, or their agglomerates can be generated by mapping Raman active elementary excitations. We measured the Raman response from carbon vibrations in SWCNTs excited by confocal scanning of a focused laser beam. Carbon vibrations reveal key characteristics of SWCNTs such as the nanotube diameter distribution (radial breathing modes (RHM). 100-300 cm-1 ) , the presence of defects and functional groups (D-mode, l300-1350 cm-1 ), strain and oxidation states of SWCNTs, as well as the metallic or semiconducting character of the tubes encoded in the lineshape of the G-modes at 1520-1600 cm-I . In addition, SWCNTs are highly anisotropic scatterers. The Raman response from a SWCNT is maximal for incident light polarization parallel to the tube axis and vanishing for perpendicular directions. We show that the SWCNT bundle shape or direction can be determined. with some limitations, from a set of Raman images taken for two orthogonal dilections of the incident light polarization.
The NIST Recommended Practice Guide on Measurement Issues in Single Wall Carbon Nanotubes represe... more The NIST Recommended Practice Guide on Measurement Issues in Single Wall Carbon Nanotubes represents the output from the 2nd NASA-NIST workshop devoted to issues of nanotube purity, dispersion and measurement techniques held at NIST in 2005. In attendance were over 80 participants, representing private corporations, universities, and government laboratories. The primary purpose of the workshop was to bring together technical and business leaders in the field of single wall carbon nanotubes (SWNTs) to discuss measurement priorities and aid in the development of measurement protocols. This guide lays out written protocols to enable product developers to more rapidly assess as-received materials, prepare quality nanotube dispersions, and ultimately achieve both repeatability and high performance in their resulting value-added devices. The technical chapters in this guide were written by leading practitioners in the field and present standard methods currently used for characterization of single wall nanotubes in a straightforward fashion. techniques, and it has traditionally been the most popular tool to evaluate the quality of as-prepared SWNT soot. (7) Because a typical SEM frame visualizes less than 10 -12 g of an inhomogeneous sample for which there is no published algorithm with which to quantify the SWNT content, the use of these techniques to assess the purity of bulk SWNT samples is not recommended.
Carbon Nanotubes represents the output from the 2nd NASA-NIST workshop devoted to issues of nanot... more Carbon Nanotubes represents the output from the 2nd NASA-NIST workshop devoted to issues of nanotube purity, dispersion and measurement techniques held at NIST in 2005. In attendance were over 80 participants, representing private corporations, universities, and government laboratories. The primary purpose of the workshop was to bring together technical and business leaders in the field of single wall carbon nanotubes (SWNTs) to discuss measurement priorities and aid in the development of measurement protocols. This guide lays out written protocols to enable product developers to more rapidly assess as-received materials, prepare quality nanotube dispersions, and ultimately achieve both repeatability and high performance in their resulting value-added devices. The technical chapters in this guide were written by leading practitio- ners in the field and present standard methods currently used for characteriza- tion of single wall nanotubes in a straightforward fashion.
The intramolecular kinetic isotope effect for the reaction O(<sup>3</sup><i>P</i>)+HD
Journal of Chemical Physics, Jun 15, 1990
The branching ratio for the reaction O(3P)+HD to produce OH and OD was measured over the temperat... more The branching ratio for the reaction O(3P)+HD to produce OH and OD was measured over the temperature range 339–500 K using a discharge-flow reactor. The OH and OD products were detected using laser-induced fluorescence under steady-state conditions. In order to determine the relative concentrations of OH and OD produced in this reaction, calibration runs were performed using the reactions of O(3P)+H2 and D2 to produce known relative amounts of the same species. Kinetic modeling showed that secondary reactions and the production of vibrationally excited OD did not affect the measured branching ratio. We found that the OH/OD ratio increased rapidly with decreasing temperature, in qualitative agreement with theory, showing that the reaction is dominated by tunneling below 400 K. At the lowest temperatures, the observed branching ratio is larger than predicted. The reason for this discrepancy is not known.
The Journal of Physical Chemistry C, 2018
We report the temperature dependence of the Electron Spin Resonance (ESR) absorption and magnetic... more We report the temperature dependence of the Electron Spin Resonance (ESR) absorption and magnetic susceptibility of plastic crystal [(CH 3) 4 N]FeCl 4. We demonstrate the extreme sensitivity of ESR to the static and dynamic structural transitions characteristic of this material. We observed a narrowing of the ESR line in the high temperature plastic-crystal phase, which is due to fast rotation (τ ≈10 −9 s) of the [FeCl 4 ] − anion. This is a rare example of the effect of fast motional narrowing in
This chapter presents an overview of the room temperature ionic liquids (RTILs), their compositio... more This chapter presents an overview of the room temperature ionic liquids (RTILs), their composition, synthesis and use in electrochemical investigations. The advantageous electrochemical properties of RTILs make them a useful alternative to conventional solvents/electrolytes for more ecofriendly, innovative and sustainable electrochemistry. A brief discussion about the electrochemical advantages, potential applications, practical concerns and future challenges in RTIL based electrochemical investigations and applications is presented in the current chapter.
Vibrational temperature from measurements of N2 and N2(+) shock layer radiation
27th Aerospace Sciences Meeting, Jan 9, 1989
ABSTRACT Measurements of the vibrational temperature in a shock layer produced by a cylindrical b... more ABSTRACT Measurements of the vibrational temperature in a shock layer produced by a cylindrical blunt body in an arc jet nitrogen flow are made for both the neutral molecule and the molecular ion. Spectra were obtained at two locations in the shock layer produced by a 20-cm long cylindrical blunt body inserted in the arc jet conical flow. The technique used for determining the temperatures from the spectral radiation involves obtaining ratios of integrated intensities for certain spectral regions of the measured spectrum and making a comparison with computed ratios as a function of temperature for the same spectral regions. The technique is difficult to apply due to radiation overlapping bands from other species. However, using a trial and error procedure, the vibrational and rotational temperatures at the two locations are inferred. The results indicate that the shock layer is significantly out of thermal equilibrium.
Nucleation and Atmospheric Aerosols, 2001
The production of isolated single wall carbon nanotubes (SWNTs) is accomplished using the laser o... more The production of isolated single wall carbon nanotubes (SWNTs) is accomplished using the laser oven process. Material is collected on quartz substrates at different locations in the laser oven for a variety of flow conditions. The lengths and diameter distributions of the nanotubes are measured directly (without additional processing steps) using AFM. Preliminary Raman data taken using 2D scans indicate the feasibility of this technique for length and diameter determination. The AFM study indicated the formation of long individual nanotubes, which then seem to coalesce into bigger bundles. The role of the inner tube of the flow-tube set up is confirmed to improve interactions between SWNTs resulting in formation of bundles. Flowing buffer gas seems to influence the dispersion of particulate material in the nanotube product.
Carbon, 2004
Single wall carbon nanotubes (SWCNTs) can be synthesized and purified by a number of techniques, ... more Single wall carbon nanotubes (SWCNTs) can be synthesized and purified by a number of techniques, and always contain certain amount of impurities of varying composition (mostly metal catalyst and non-tubular carbon), as well as defects resulting from purification. Particular purification route also affects homogeneity of nanotube material and its dispersability in organic solvents, which are important in the subsequent application development. A number of analytical characterization tools have been used successfully in the past years to access various properties of nanotube materials, but lack of standards makes it difficult to compare these measurements across the board. In this work we report on the protocol which standardizes measurements in TEM, SEM, TGA, Raman and UV-VIS spectrometer, consumes <30 mg of material, and was found to provide fast and reliable feedback in the development of purification techniques. The amount of residual metal catalyst is determined directly, and numerical measures are established for parameters such as homogeneity, thermal stability and dispersability, to allow easy comparison of SWCNT materials. Quantitative measurement of non-tubular carbon impurities still remains a problem, and we have to rely on qualitative electron microscopy observations.
Production and measurements of individual single-wall nanotubes and small ropes of carbon
Applied Physics Letters, Mar 12, 2001
This work focuses on the size and spatial dependence of single-wall carbon nanotubes produced by ... more This work focuses on the size and spatial dependence of single-wall carbon nanotubes produced by the pulsed-laser vaporization technique. The study indicates that very long (tens of microns) individual nanotubes form in the vicinity of the target, and subsequently coalesce into bundles. The role of the inner flow tube is confirmed to restrict plume expansion and improve interactions between carbon atoms resulting in nanotube and rope formation. The effect of the flowing buffer gas seems to influence the dispersion of particulate contaminant material in the nanotube product. More particulate matter is produced at lower oven temperatures.
Physical Review Letters, Jun 12, 2000
The mechanical response of 15 single wall carbon nanotube (SWCNT) ropes under tensile load was me... more The mechanical response of 15 single wall carbon nanotube (SWCNT) ropes under tensile load was measured. For 8 of these ropes strain data were obtained and they broke at strain values of 5.3% or lower. The force-strain data are well fit by a model that assumes the load is carried by the SWCNTs on the perimeter of each rope. This model provides an average breaking strength of SWCNTs on the perimeter of each rope; the 15 values range from 13 to 52 GPa (mean 30 GPa). Based on the same model the 8 average Young's modulus values determined range from 320 to 1470 GPa (mean 1002 GPa).
Modified carbon nano structures for energy and display applications
Carbon nano structures including fullerenes, nanotubes, nanocones and graphene are gaining a cons... more Carbon nano structures including fullerenes, nanotubes, nanocones and graphene are gaining a considerable interest for supercapaitors in memory backup devices, electric vehicles, and emergency power supplies. In addition, these structures are utilized to improve resolution and power consumption of field emission displays. The energy density and performance of supercapacitors depend on the choice of electrode and electrolyte materials. Our recent
Nanoscale, 2014
We investigate charge transport in a chemically reduced graphene oxide (RGO) film of sub-micron t... more We investigate charge transport in a chemically reduced graphene oxide (RGO) film of sub-micron thickness. The I-V curve of RGO film shows current switching of the order of $10 5 above the threshold voltage. We found that the observed I-V curve is consistent with quantum tunnelling based charge transport. The quantum tunnelling based Simmons generalized theory was used to interpret the charge transport mechanism which shows that the current switching phenomenon is associated with transition from direct to Fowler-Nordheim (F-N) tunneling. The absence of current switching in the I-V curve after stripping away the oxygen functional groups from chemically RGO film confirms that the presence of these groups and reduced interaction between adjacent layers of RGO play a key role in charge transport. Such metal-based current switching devices may find applications in graphene-based electronic devices such as high voltage resistive switching devices.
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Papers by Sivaram Arepalli