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The dynamics of dissociation and negative ion formation have been investigated for the hyperthermal energy scattering of state-selected OCS+(X 2Πx, υ1, υ2, υ3) on Ag(111). Experiments reveal the effect that collision energy and internal energy have on the formation of scattered ionic products. An analysis of the appearance threshold and fragment velocity distribution for each scattered product channel [S−(2P), O−(2P), and SO−(X 2Π)] suggests that three distinct fragmentation mechanisms compete. Prompt impulsive dissociation of neutralized OCS+(X 2Π), followed by electron attachment to the nascent O fragment, is responsible for O−(2P) emergence. The production of SO−(X 2Π) relies on a collisionally activated distortion of OCS, forcing the O and S atoms close together while ejecting the central carbon atom. Finally, a comparison between the scattering of state-selected OCS+(X 2Πx, υ1, υ2, υ3) and S+(4S) on Ag(111) provides strong evidence that dissociative neutralization of OCS+(X 2Πx, υ1, υ2, υ3) leads to ...

The processes of electron transfer and dissociative scattering are explored for collisions of state-selected hyperthermal energy (5–80 eV) NO+(X1Σ+, ν) on GaAs(110) and Ag(111). In conjunction with classical and quantum mechanical calculations, the experimental data reveal the sequence of neutralization, dissociation, and electron attachment steps responsible for the emergence of O−(2P) ions. This mechanism is compared to those which govern the formation of negative ion fragments in the scattering of state-selected OCS + (X 2 II 3 2 ) on Ag(111). In the scattering of OCS+, impulsive mechanical dissociation forms O−(2P) ions; dissociative neutralization leads to S−(2P); and atom elimination yields SO−(2II).

Recently reported molecular ion/surface scattering experiments suggest that translational and vibrational energies each have a distinct influence on molecular dissociation for the NO+/GaAs(110) system [J. Chem. Phys. 1994, 100, 6791]. To interrogate the coupling between vibrational and translational degrees of freedom, classical trajectory simulations were performed. The dissociation dynamics and energy transfer processes were examined for three different molecule/surface repulsive potentials: a Born−Mayer potential, a Ziegler−Biersack−Littmark potential, and a Hartree−Fock potential. In each case, the calculated product appearance thresholds and average product translational energies are qualitatively consistent with the aforementioned experimental results. In all, this suggests that translational energy activates dissociation via a collision-induced dissociation mechanism. Regarding initial molecular vibrational energy, the classical model shows that the relative dissociation probability depends on vib...

The processes of electron transfer and dissociative scattering are explored for collisions of hyperthermal NO + on GaAs(110). The experiments reveal a marked angular dependence to O − emergence. A strong correlation between the O − scattering angle and the final atom-surface interaction site provides a map of the lateral dependence to reactivity. The results are modeled by sequential neutralization, dissociation, and electron attachment steps. Classical trajectory calculations, in conjunction with an empirical opacity function, accurately reproduce the experimental results. The opacity function is interpreted as the probability that an electron will attach to a departing O fragment as a function of the last surface site the atom impacts. The experiments indicate that O − emergence occurs predominantly for oxygen atoms which come in close contact with the localized dangling bond states of GaAs(110).

Hyperthermal energy reactions of NO+ with Ag(111) were studied as a function of collision energy and the incident diatom’s internuclear‐axis direction. Laser photoselection via (1+1’) resonance enhanced multiphoton ionization (REMPI) prepared an aligned distribution of NO+(X 1Σ+, Etrans, v=0, J) prior to the molecules impact with the surface. The emergence of scattered O− products was enhanced when NO+ approached the surface with an ‘‘end‐on’’ rather than a ‘‘side‐on’’ orientation. Moreover, the magnitude of the reaction’s alignment preference increased with decreasing collision energy. The appearance threshold for O− was approximately 20 eV. Classical trajectory calculations demonstrated that these results are consistent with a collision‐induced dissociation mechanism mediated by both vibrational and rotational excitation upon impact. Reorientation of the internuclear axis during the collision drastically affects the simulated dissociation dynamics. No alignment preference for scattered NO− emergence cou...

The reactivity of a molecule striking a surface was found to depend on the diatom's internuclear-axis alignment. State-selected NO+ (X1Σ+, v = 0, J) reagents were aligned through laser ionization prior to their impact with a Ag(111) surface. The yield of scattered O− products was enhanced by “end-on” type collisions, and this preference diminished as the collision energy increased from 35 to 80 eV. Classical trajectory calculations showed that a collision-induced dissociation model is consistent with the experimental observations.

The scattering of state‐selected NO+(X 1Σ+, v=0–6) on GaAs(110) was explored across the hyperthermal energy region. Relative yields and velocity distributions for scattered anionic products NO−(X 3Σ−, v=0) and O−(2P) were measured as a function of the number of vibrational quanta and collision energy for NO+(X 1Σ+, v=0–6) incident on the surface. Facile neutralization along the inbound trajectory forms vibrationally excited NO(2Π) immediately prior to surface impact. Electron attachment to form NO−(X 3Σ−, v=0) occurs near the distance of closest approach between the molecule and surface. With regard to O−(2P) emergence, a collision‐induced dissociation mechanism is consistent with the observed 25 eV threshold. Incident vibrational energy is as much as ten times more effective than translational energy in forming O−(2P). This paper represents the first experimental investigation into the effect of vibrational energy on electron transfer and dissociation of ions at surfaces and highlights the unique interpl...

A hyperthermal beam of state‐selected NO+ X Σ+(v=0–6) ions is scattered on a clean, well‐characterized GaAs(110) surface. The threshold for the appearance of scattered O− ions occurs at a collision energy of 25 eV. Vibrational energy proves to be an order of magnitude more effective than translational energy in enhancing the yield in this channel.

LLNL has utilized optical parametric oscillator technology to develop and field a rapidly-tunable mid-wave IR DIAL system. The system can be tuned at up to 1 KHz over the 3.3- 3.8 micron spectral region, where hydrogen-bond stretching modes provide spectroscopic signatures for a wide variety of chemicals. We have fielded the DIAL system on the LLNL site on range, turbulence, and receiver aperture size. In this paper we describe the interplay of turbulence and speckle to produce the observed nose fluctuations at short range.

We have utilized resonance-enhanced multiphoton ionization in conjunction with ion optics to produce state-selected NO+(X1(Sigma) +, v equals 0 - 6, Etrans equals 8 - 80 eV) ions.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Supplemental calcium supplied foliariy as Ca glutarate, soil incorporated as gypsum, fertigated as CaNO3, in 3-way combination, or none at all, had no effect on fruit firmness, as measured by shear, reduced fruit decay by as much as 23%. over controls (1986-1988), and generally improved fruit Ca levels only in the combination treatment of 904 kg/ha. Fruit raw product quality (pulp pH, acidity, soluble solids concentration, and Hunter color values) were not consistently affected, although there were significant interactions between cvs Fern and Cardinal, harvest dates, holding time, and years. Supplemental Ca reduced fruit size, but tended to increase yield. In 1988, individual fruits were partitioned into upper/lower, dermal/interior, and upper/lower seeds (6 parts), Ca was the third most abundant mineral nutrient in receptacle tissue, but most abundant in seeds. Highest Ca levels were found (descendingly) in the seed, dermal, and interior pulp tissue, Ca was higher in the upper (stem) end. Differences in fruit Ca levels between cvs were found in the seeds and not the receptacle. No clear relationship was observed between fruit firmness, decay, and Ca level.

The first clear experimental demonstration, to our knowledge, is reported of large amplification of small-scale spatial perturbations by stimulated thermal Rayleigh scattering of a cw laser beam propagating through an absorbing medium in a context normally associated with thermal blooming. A single-mode argon-ion laser beam with λ = 488 nm was propagated vertically downward through a 1.2-m cell filled with CCl4 that was doped with an absorber to have optical depths in the range 0.5–2.3. A shear-plate interferometer near the cell input generated the perturbation. Fringe growth was rapid and visually obvious, as was competing growth from dust specks, etc. The measured growth rate is in good agreement with the asymptotic rate from analytic stimulated thermal Rayleigh scattering theory.

Fruit of `Cardinal' and `Fern' were harvested, acid washed, decapped, and frozen to -20° C on 6 May 88. Frozen fruits were subsequently divided into six parts. The upper and lower fruit halves were further separated into pulp, dermal, and seed components. Nutrients increased from the pulp to the seed with the exception of Al. K was most abundant in receptacle tissue (but not in seeds) followed by P, Ca, and Mg. K, Ca, Mg, and Cu were higher and Mn and Zn lower in pulp upper tissue than lower pulp tissue. K, Ca, Na, Zn, and A1 were higher in upper dermal tissue than in lower dermal tissue. Ca, Cu, and B were higher and Mg and Mn lower in upper octanes than in lower achenes. In descending order, Ca, P, Mg, and K were the most abundant seed nutrients. Supplementing strawberries with 904 Kg Ca/ha increased only the seed Ca levels. All levels of supplemental pre-harvest Ca were found to reduce postharvest decay. Although `Fern' was higher in seed Ca, with similar Ca levels in receptacle tissue, fruit decay was higher than in `Cardinal'. There appears to be no clear relationship between fruit decay and Ca distribution within the fruit.

We have examined the monomer-polymer equilibria which form the cytoskeletal polymers in squid axoplasm by extracting protein at low concentrations of monomer. The solution conditions inside the axon were matched as closely as possible by the extraction buffer (buffer P) to preserve the types of protein associations that occur in axoplasm. Upon extraction in buffer P, all of the neurofilament proteins in axoplasm remain polymerized as part of the stable neurofilament network. In contrast, most of the polymerized tubulin and actin in axoplasm is soluble although a fraction of these proteins also exists as a stable polymer. Thus, the axoplasmic cytoskeleton contains both stable polymers and soluble polymers. We propose that stable polymers, such as neurofilaments, conserve cytoskeletal organization because they tend to remain polymerized, whereas soluble polymers increase the plasticity of the cytoskeleton because they permit rapid and reversible changes in cytoskeletal organization.

The effect of ten species of ion-implanted impurities on the thermal oxidation of copper has been studied. The majority of these increased the oxidation resistance of the copper, the greatest effect (85% decrease in oxidation) being caused by Ti. Only Xe and Cs caused significantly increased oxidation in dry oxygen, but in the presence of water vapour the effect of Ti+ implants was reversed and increases in oxidation rate up to 100% were observed. Electrical measurements on devices formed by applying a gold probe to the oxide surface showed a correlation between switching voltage and the effect of the implant on the oxidation rate. A simple model is proposed whereby the observed behaviour is ascribed to the creation of an n type region in the predominantly p type oxide such that inward hole diffusion is inhibited during oxide growth.

Temporal (vertical) and spatial trends in sediment accumulations of nonresidual aluminum, manganese, lead, zinc, copper, and nickel were investigated in 18 core samples collected from four of the Turkey Lakes in 1980–81. Accumulation rates of nonresidual Al differed among sampling sites, both within and among lakes, but was assumed to have been temporally constant at each location. Concentrations of dry matter and all other metals were expressed as mass per unit mass of Al. Cumulative Al was used as an index of time. Since Mn enrichments near the sediment surface may reflect an oxidation zone, they were not interpreted as increased Mn inputs. Other metal enrichments were considered anthropogenic. Little Pb occurred at the bottom of sediment cores, but Pb accumulation rates increased greatly towards the sediment surface. Major Pb enrichments were assumed to have begun at 1940. Zn accumulation rates had also progressively increased through most of the previous four decades. During the same period, there was a modest rise in Cu and Ni accumulation rates. Metal accumulation rates differed considerably among lakes, and among sites within lakes, but these differences primarily reflected variations in dry matter sedimentation rates.

Elevated levels of Ni, Cu, and Zn are present in surficial sediments of lakes in the Sudbury region of northeastern Ontario. Metal concentrations in sediments were highest in lakes closest to local smelters, and decreased rapidly with distance: equations are presented describing these relationships. Several fish species were collected from a series of these metal-contaminated lakes, and analyzed for metal content of muscle, liver, and kidney tissues. Muscle tissue was a poor indicator of increased metal availability. Liver tissue was a good indicator for Cu, while kidney tissue was best for Ni. Zinc levels in tissues varried little among either fish species or lakes. The presence of elevated levels of Cu in liver, and elevated levels of Ni in liver and kidney tissues of fish from certain lakes supported the hypothesis that some fish populations were being stressed by metal additions to local aquatic habitats. Although the degree of lake contamination (as indicated by Cu concentrations in sediments) was one factor influencing Cu availability, water quality parameters such as alkalinity and DOC also appeared to be very important.

A vapour phase bromination procedure using80mBr and82Br has been investigated for reaction with unsaturated lipids present in a fingerprint deposit. The reaction is rapid and in combination with autoradiography provides a promising technique for the visualisation of latent fingerprints particularly under conditions which preclude the application of other methods. Preliminary work on the degradation of fingerprint constituents by UV and water is reported with comparative studies using the35SO2 reaction.