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1

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Polymer microparticle arrays from electrodynamically focused microdroplet streams (2000)

Ng, K. C. ; Ford, J. V. ; Jacobson, S. C. ; [et al.]

[S.l.] : American Institute of Physics (AIP)

Review of Scientific Instruments 71 (2000), S. 2497-2499

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ISSN: 1089-7623

Source: AIP Digital Archive

Topics: Physics , Electrical Engineering, Measurement and Control Technology

Notes: We describe instrumentation for forming two-dimensional arrays of polymer microparticles produced from electrodynamically focused microdroplet streams. A single-stage linear quadrupole was used to focus droplets/particles onto silanated glass slides mounted on a computer-driven two-dimensional translation stage. Center-to-center position stability was on the order of 1 μm. Applications to molecular sorting with polymer particles as host carriers are discussed. © 2000 American Institute of Physics.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1063/1.1150642

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2

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Femtosecond dissociation dynamics of methyl iodide clusters (1998)

Poth, L. ; Zhong, Q. ; Ford, J. V. ; [et al.]

College Park, Md. : American Institute of Physics (AIP)

The Journal of Chemical Physics 109 (1998), S. 4791-4797

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ISSN: 1089-7690

Source: AIP Digital Archive

Topics: Physics , Chemistry and Pharmacology

Notes: The photodissociation dynamics of methyl iodide clusters using λ=270 nm as pump and λ=405 nm as probe are studied using a femtosecond two color pump–probe laser arrangement combined with a reflectron time-of-flight (RTOF) mass spectrometer. This enables the A˜ state and 10s Rydberg state of methyl iodide to be accessed with the pump beam. Of particular interest is a comparison of the femtosecond dynamics of the methyl iodide monomer with the clustered species. Clocking of the monomer dissociation shows a transient which is indicative of a fast C–I bond breakage as is to be expected upon excitation of methyl iodide into the fast dissociating A˜ state, or into the predissociative 10s Rydberg state. Clusters, however, show a very different pump–probe transient composed of a fast decay and a subsequent dip in ion signal followed by a rise for pump–probe delay times greater than 2 ps. The cluster ion signal shows an enhancement for pump probe delay times up to 70 ps. The results are interpreted in terms of the electronic state diagram of the methyl iodide monomer and effects resulting from clustering of these species, shifts of electronic energy levels and caging of excited species in the cluster. © 1998 American Institute of Physics.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1063/1.477090

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Femtosecond laser interactions with methyl iodide clusters. I. Coulomb explosion at 795 nm (1999)

Ford, J. V. ; Zhong, Q. ; Poth, L. ; [et al.]

College Park, Md. : American Institute of Physics (AIP)

The Journal of Chemical Physics 110 (1999), S. 6257-6267

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ISSN: 1089-7690

Source: AIP Digital Archive

Topics: Physics , Chemistry and Pharmacology

Notes: The study of the interaction of femtosecond laser radiation with matter, especially clusters, has blossomed in recent years due to advances in laser technology. One aspect of this interaction is Coulomb explosion. This effect occurs when the repulsive energy of like charges, known as Coulomb repulsion, overcomes the cluster's total cohesive energy, causing the cluster to disintegrate into charged fragments. In this study, the interactions of methyl iodide clusters, formed in a supersonic expansion using argon and helium as carrier gases, were investigated at 795 nm using a Ti:Sapphire femtosecond laser. The resulting atomic and cluster ions were analyzed in a reflection time-of-flight mass spectrometer. The focus of these studies was the elucidation of the effects of carrier gas and laser wavelength on the laser-cluster interactions leading to Coulomb explosion. To achieve these goals, the effects of different carrier gases, laser power, cluster distribution, and the resulting Coulomb explosion energies were examined. A secondary consideration was to examine the experimental results with regard to the Coherent Electron Motion and Ionization Ignition models. © 1999 American Institute of Physics.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1063/1.478530

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4

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Water clusters: Contributions of binding energy and entropy to stability (1993)

Shi, Z. ; Ford, J. V. ; Wei, S. ; [et al.]

College Park, Md. : American Institute of Physics (AIP)

The Journal of Chemical Physics 99 (1993), S. 8009-8015

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ISSN: 1089-7690

Source: AIP Digital Archive

Topics: Physics , Chemistry and Pharmacology

Notes: The binding energies of water cluster cations are obtained by measuring decay fractions of metastable dissociation and employing Klots' model of evaporative dissociation. Their variation with degree of solvation shows the commonly observed decrease, followed by a slow rise in magnitude, which typifies the trend found for solvated cations. There is no observed abrupt change in the vicinity of the well-known magic number (H2O)21⋅H+ corresponding to (H2O)20⋅H3O+. Other data are used to deduce free energies for water clusters up to size n=28, allowing a determination of entropy changes with size. All of the thermochemical data, including prior literature values, are assessed in terms of calculations made using the liquid drop model and standard statistical mechanical equations. It is concluded that entropic rather than energetic effects give rise to the referred to magic number.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1063/1.465678

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Refractive index dispersion functions of solid-phase polymers by multicolor optical diffraction (2000)

Ford, J. V. ; Sumpter, B. G. ; Noid, D. W. ; [et al.]

Woodbury, NY : American Institute of Physics (AIP)

Applied Physics Letters 77 (2000), S. 2515-2517

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ISSN: 1077-3118

Source: AIP Digital Archive

Topics: Physics

Notes: We show that fourth-order dispersion functions of solid-phase polymers can be determined by multicolor optical diffraction. Electrodynamically trapped microparticles of polyethylene glycol with different molecular weights were probed by two-dimensional optical diffraction with four different laser wavelengths (632.8, 514.5, 488.0, and 457.9 nm); subsequent Mie analysis of one-dimensional scattering patterns yielded size and refractive index (both real and imaginary parts). Using a single wavelength as a size reference, the nonlinear dependence of the refractive index of solid (nonevaporating) polymer microparticles was determined by finding the refractive index for a given wavelength that best matched a Mie calculation subject to the reference size constraint. The experimentally determined refractive index values were fit to a standard fourth-order Cauchy function to obtain values for n0, n1, and n2. © 2000 American Institute of Physics.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1063/1.1318940

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