Harpooning

NakatsujI H, Kuwano R, Merita H and Nakal H 1993 Dipped adcluster model and SAC-CI method applied to harpooning, chemical luminescence and electron emission in halogen chemisorption on alkali metal surface J. Mol. Catal. 82 211-28... 

The cosmopolitan was a kind of fast debutante that showed up in the 1980s and 1990s—the Cornelia Guest of cocktails. Many people claimed it, like dates who had been dumped at a club. (Ocean Spray, the cranberry juice bottler, already had on the books a very similar drink, the Harpoon. What s in a name —celebrity, or nothing.)... 

In the harpoon mechanism for the reaction between potassium and iodine to form potassium iodide, as a K atom approaches an I, molecule (a), an electron passes from the K atom to the I, molecule (b). The charge difference now tethers the two ions together (c and d) until an I ion separates and leaves with the Kf ion (e). 

The possibility of a barrier which inhibits a reaction in spite of the attractive ion-dipole potential suggests that one should make even crude attempts to guess the properties of the potential hypersurface for ion reactions. Even a simple model for the long range behavior of the potential between neutrals (the harpoon model ) appears promising as a means to understand alkali beam reactions (11). The possibility of resonance interaction either to aid or hinder reactions of ions with neutrals has been suggested (8). The effect of possible resonance interaction on cross-sections of ion-molecule reactions has been calculated (25). The resonance interaction would be relatively unimportant for Reaction 2 because the ionization potential for O (13.61 e.v.) is so different from that for N2 (15.56 e.v.). A case in which this resonance interaction should be strong and attractive is Reaction 3 ... 

The cx)ne snails are predatory, venomous molluscs which use a common general strategy to capture prey (i, 5-7). All 300-500 species of Conus have a specialized venom apparatus, diagrammed in Figure 1 (8). A venom paralytic to the prey is produced in a venom duct and injected through a disposable, harpoon-like tooth (Figure 2). Paralysis of the prey can be remarkably rapid in the case of certain piscivorous cone species, the fish prey is immobilized in less than one second. 

Figure 1. Diagram of the venom duct of Conus. The venom is produced in the venom duct, apparently expelled from the duct into the proboscis by contraction of the venom bulb. Simultaneously, a harpoon-like tooth is transferred from the radula sac to the proboscis. When injection takes place, the venom is pushed through the hollow tooth and flows into the prey through a hole at the tip of the tooth. Typically, fish-hunting cones will strike at a fish only once and grasp the tooth after injection has occurred, effectively harpooning their prey while injecting the paralytic venom. In contrast, snail-hunting cones will usually sting their prey several times before total paralysis occurs. (Reprinted with permission from the Second Revised Edition of Ref. 8. Copyright 1988 Darwin Press, Inc.)...

Figure 2. The harpoon-like tooth of Conus, a. An unusual photograph of a radular tooth at the tip of the proboscis of Conus pur-purascens. Normally, the tooth would not be ejected from the proboscis until the prey had been harpooned. Photograph by Alex Ker-stitch. b. A scanning electron micrograph of the tip of the radular tooth of Conus purpurascens, showing its harpoon-like form.

In summary, preliminary experiments have demonstrated that the efficiency and outcome of electron ionization is influenced by molecular orientation. That is, the magnitude of the electron impact ionization cross section depends on the spatial orientation of the molecule widi respect to the electron projectile. The ionization efficiency is lowest for electron impact on the negative end of the molecular dipole. In addition, the mass spectrum is orientation-dependent for example, in the ionization of CH3CI the ratio CHjCriCHj depends on the molecular orientation. There are both similarities in and differences between the effect of orientation on electron transfer (as an elementary step in the harpoon mechanism) and electron impact ionization, but there is a substantial effect in both cases. It seems likely that other types of particle interactions, for example, free-radical chemistry and ion-molecule chemistry, may also exhibit a dependence on relative spatial orientation. The information emerging from these studies should contribute one more perspective to our view of particle interactions and eventually to a deeper understanding of complex chemical and biological reaction mechanisms. 

Harpoon Antiship Missile (US Navy). THE NAVY S HARPOON ANTISHIP MISSILE (McDonnell Douglas) has completed six of twenty scheduled full-scale flight tests following many launchings to test techniques and components (CD, October 1972). Harpoon has been fired successfully in its basic form from aircraft with a 300-pound, 30-inch booster from surface ships and from submarine torpedo tubes, with folded wings and booster enclosed in a buoyant capsule... 

Cone snails are found in tropical waters, often in the neighborhood of coral reefs. These molluscs produce a complex venom delivered through a specialized radular tooth that serves as a harpoon to immobilize their prey (Olivera et al., 1990 1991). Complete immobilisation of the prey takes only a few seconds (Terlau et al., 1996). The venom from a single cone snail can contain up to 200 different biologically-active components (review Shen et al., 2000). The primary structure of the naturally-occurring co-conopeptides derived from several species of Conus are... 

The product we monitor is again the I atom using femtosecond-resolved mass spectrometry (the other product is the Bzl species). We also monitor the initial complex evolution. The initial femtosecond pulse prepares the system in the transition state of the harpoon region, that is, Bz+h. The iodine atom is liberated either by continuing on the harpoon PES and/or by electron transfer from iodine (I2-) to Bz+ and dissociation of neutral I2 to iodine atoms. We have studied the femtosecond dynamics of both channels (Fig. 17) by resolving their different kinetic energies and temporal behavior. The mechanism for the elementary steps of this century-old reaction is now clear. 

Figure 17. (a) Generic reaction path for charge transfer reactions with both channels of harpooning and electron transfer indicated. Molecular dynamics of the Bz/l2 bimolecular reaction is shown at the bottom, (b) Observed transient for the Bz/l2 reaction (I detection) and the associated changes in molecular structure. Note that we observe the two channels of the reaction, shown in (a), with different kinetic energies and rises of the I atom. 

The results, which are detailed elsewhere, reveal that the transition state of CT reactions can be studied directly at well-defined impact geometries. The dissociative CT reaction of benzenes with iodine occurs with an elementary harpoon/electron transfer mechanism. The time scales for the CT and for the product (I) formation define the degree of concertedness and, as reported elsewhere, are significant to the recent elegant studies in condensed media by Wiersma and colleagues and by Sension. So far we have studied the electron donors of benzene, toluene, xylene, mesitylene, and cyclohexane and we plan extension to other systems. We have also studied the effect of solvation in clusters and in solutions. 

The above CT systems represent the case for intermolecular electron transfer. There is some analogy to proton transfer in acid-base reactions [5]. We have also examined intramolecular electron transfer systems and studied the influence of IVR and geometric changes this work is detailed elsewhere [5]. Other reactions involving ultrafast electron transfer are those of harpooning in Xe + I2) Nal, and more recently Xe/Ch (see Ref. 1). 

Transition States of Charge-Transfer Reactions Femtosecond Dynamics and the Concept of Harpooning in the Bimolecular Reaction of Benzene with Iodine, P. Y. Cheng, D. Zhong, and A. H. Zewail, J. Chem. Phys. 103, 5153 (1995). 

Manifestations of nuclei tunneling in chemical reactions in gaseous, liquid, and solid phases are consecutively considered in Sects. 4.2-4.5. Also discussed in this chapter are (1) manifestations of nuclear tunneling in the vibrational spectra of ammonia-type molecules (Sect. 4.6), (2) electron tunneling in gas-phase chemical reactions of atom transfer (the so-called "harpoon reactions, Sect. 4.2), and (3) tunneling of hydrated electrons in the reactions of their recombination with some inorganic anions in aqueous solutions (Sect. 4.4). 

Harpoon reactions of alkaline metal atoms with halogen molecules in the gas phase seem to be the first instance of the observation of chemical electron transfer reactions at distances somewhat exceeding gas-kinetic diameters. Actually, as far back as 1932, Polanyi, while studying diffusion flames found for these reactions cross-sections of nR2, somewhat exceeding the gas-kinetic cross-sections [69]. Subsequently, more precise measurements which were carried out in the 1950s and 1960s with the help of the molecular beam method, confirmed the validity of this conclusion [70],... 

For harpoon reactions of alkaline metal atoms with iodine molecule I2, the interaction radii, Re, calculated using the formula Re = (ajji) 12 from the experimentally measured cross-sections a, are compared in Table 3 with the distances, Ru, calculated with the help of eqn. (40) and the sums of the gas-kinetic radii i M + i l2 of the reagents. In these calculations, effective radii of alkaline metal atoms have been used as RM, while the radii of the molecule I2, calculated from the data on the viscosity of I2 vapour at T > co and at T = 273 K, have been used as i l2 (the values of RM + i ,2 given in brackets correspond to the latter) [71], It is seen that the values of Re exceed Rm + Rh, i.e. electron transfer occurs at large impact parameters. 

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