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Fragment rotational state distributions from the dissociation of NeIBr: Experimental and theoretical results (1992)

Stephenson, Thomas A.

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

The Journal of Chemical Physics 97 (1992), S. 6262-6275

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ISSN: 1089-7690

Quelle: AIP Digital Archive

Thema: Physik , Chemie und Pharmazie

Notizen: The IBr fragment rotational state distributions that result when the NeIBr van der Waals molecule undergoes vibrational predissociation have been measured in a pump–probe laser-induced fluorescence experiment. Independent of initial vibrational state and the number of quanta of vibrational energy lost from the I–Br coordinate, the rotational distributions extend over the full range of energetically accessible states. From the observation of energetic constraints on the rotational distribution, the dissociation energy (D0) is calculated to be 65.5±1.2 cm−1 for the A electronic state, v=16. For the X electronic state, v=0, D0=71.8±1.2 cm−1. Quantum mechanical bound state calculations carried out on a model A electronic state potential energy surface are in quantitative agreement with this result. The rotational distributions are broader than that predicted by either a Franck–Condon or classical impulsive model for the dissociation. The distributions are qualitatively in accord with classical trajectory calculations. Analysis of specific rotational distributions in the context of the energy gap law shows poor quantitative agreement. The average fragment rotational energy relative to analogous Ne-containing complexes is, however, qualitatively predicted by the energy gap relations.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.463688

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Digitale Medien

Vibrational branching ratios from the dissociation of the NeIBr van der Waals molecule (1992)

Walter, Sarah A. ; Stephenson, Thomas A.

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

The Journal of Chemical Physics 96 (1992), S. 3536-3541

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ISSN: 1089-7690

Quelle: AIP Digital Archive

Thema: Physik , Chemie und Pharmazie

Notizen: The degree of vibrational excitation in the IBr fragment from the vibrational predissociation of NeIBr (A 3Π1) has been measured using two-color pump–probe laser-induced fluorescence spectroscopy. We find that for the lowest initial vibrational states examined, Δv=−1 dissociation pathways dominate the dynamics, while this channel is closed for v≥17. From this result, the A state binding energy (D0) of the complex is determined to be 67±4 cm−1, while that in the X electronic state is found to be 73±4 cm−1. The X state binding energy is identical to that for NeI2 and NeBr2, suggesting that the potential energy surface for NeIBr can be constructed from a summation of atom–atom pair potentials; we present such a model potential energy surface. The variations in the vibrational branching ratios, when combined with the trends in the predissociation rates, point to the importance of fragment rotational excitation in the dynamics of the dissociation.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.461908

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Digitale Medien

Nascent product states in the photoinitiated reaction of O3 and H2O (1992)

Sauder, Deborah G. ; Stephenson, John C. ; King, David S. ; [weitere]

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

The Journal of Chemical Physics 97 (1992), S. 952-961

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ISSN: 1089-7690

Quelle: AIP Digital Archive

Thema: Physik , Chemie und Pharmazie

Notizen: The rotational, vibrational and fine-structure state distributions for the reaction 16O(1D)+ H218O →16OH +18OH, triggered by 266 nm photolysis of O3, have been measured under conditions where less than 1% of the nascent fragments experienced collisions prior to detection. The distributions are qualitatively different than those reported earlier for 266 nm photolysis, which were evidently affected by collisions. The rotational and vibrational state distributions are similar to recent 248 nm photolysis experiments, but with differences attributed to collisional and/or energetic effects in those experiments. The "new'' 16OH is formed with vibrational populations in the ratio 0.39(v=0):0.29(v=1):0.3(v≥2). Gaussian rotational energy distributions peaked near N=12 give average rotational energies of 〈Erot〉 = 3440 and 2780 cm−1 for 16OH v=0 and v=1, respectively. The "old'' 18OH is much colder with vibrational populations 0.94(v=0):0.06(v=1) and a 18OH v=0 Gaussian rotational energy distribution characterized by 〈Erot〉 = 1920 cm−1.There is negligible rotational alignment of the 16OH fragments [βμJ' = β20(02) = 5A(0)2/4 = 0.06± 0.09], which is significantly less than expected for fragment rotations aligned with respect to the O+H2O relative velocity vector. The spin-orbit propensities deviate slightly from the statistical expectation and are characterized by [F2,N]/[F1,N]=(0.89±0.06) ×N/(N + 1). The Λ-doublet distributions for 18OH (all N) and 16OH (low-to-moderate N) fragments conform to an unconstrained-dynamics prior distribution. A slight propensity for Π(A') in excess of this expectation is seen for the 16OH (high N) fragments. These new results are discussed in terms of possible insertion and abstraction mechanisms for the reaction.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.463198

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Digitale Medien

The extraction of signal to noise values in x-ray absorption spectroscopy : Proceedings of the 4th international conference on synchrotron radiation instrumentation (1992)

Dent, A. J. ; Stephenson, P. C. ; Greaves, G. N.

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

Review of Scientific Instruments 63 (1992), S. 856-858

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ISSN: 1089-7623

Quelle: AIP Digital Archive

Thema: Physik , Elektrotechnik, Elektronik, Nachrichtentechnik

Notizen: The assessment of signal to noise (S/N) values in x-ray absorption spectroscopy is important for a number of reasons. Two methods will be described that remove the signal to give the noise. The first uses polynomials and the second Fourier filtering. Having extracted the noise the signal can then be used to calculate the S/N ratio. The method described operates on a background subtracted spectrum and is quick so it can be done on line in an experimental situation.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.1142627

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Digitale Medien

Gallium arsenide surface reconstructions during organometallic vapor-phase epitaxy (1992)

Lamelas, F. J. ; Fuoss, P. H. ; Imperatori, P. ; [weitere]

Woodbury, NY : American Institute of Physics (AIP)

Applied Physics Letters 60 (1992), S. 2610-2612

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ISSN: 1077-3118

Quelle: AIP Digital Archive

Thema: Physik

Notizen: In situ surface x-ray scattering studies of the GaAs(001) surface were used to determine whether specific surface reconstructions occur during organometallic vapor-phase epitaxy. Prior to growth, we find that surfaces heated in the presence of As form a c(4×4) structure, while those heated in the absence of organometallics or in Ga form two similar fourfold reconstructions. We find no evidence for the presence of any surface reconstruction during the actual layer-by-layer growth process.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.106924

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The first record of a myxomycete from subantarctic Macquarie Island (1992)

Stephenson, Steven L. ; Seppelt, Rodney D. ; Laursen, Gary A.

Cambridge University Press

In: Antarctic Science. 1992; 4(4): 431-432. Published 1992 Dec 01. doi: 10.1017/s0954102092000634.

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Publikationsdatum: 1992-12-01

Beschreibung: Myxomycetes (plasmodial slime moulds) are best known from temperate and boreal forests, where they are commonly found in association with decaying coarse woody debris and leaf litter on the forest floor (Martin & Alexopoulos 1969). There have been only a few reports of myxomycetes from either the continent of Antarctica or the subantarctic islands. In what apparently represents the first record of a myxomycete from the south polar region, Horak (1966) described a new species, Diderma antarcticolum Horak, from material collected on the Antarctic Peninsula (64°53′S, 62°53′W). Later, Ing & Smith (1980,1983) reported Didymium dubium Rost., Lamproderma arcyrioides (Sommerf.) Rost., Stemonitopsis (Comatricha) subcaespitosa (Peck) Nann.- Brem. and Diderma niveum (Rost.) Macbr. from South Georgia (54–55°S, 36–38°W). They also indicated that the latter species was known from Signy Island, South Orkney Islands (60°43′S, 45°36′W) and the Antarctic Peninsula (65°16′S, 64°08′W) as well as South Georgia.

Print ISSN: 0954-1020

Digitale ISSN: 1365-2079

Thema: Biologie , Geographie , Geologie und Paläontologie