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Showing papers by "Bielefeld University published in 1986"


Journal ArticleDOI
TL;DR: In this paper, the temperature dependence of the screening radius, as obtained from lattice QCD, is compared with the J/ψ radius calculated in charmomium models, and the feasibility to detect this effect clearly in the dilepton mass spectrum is examined.

2,416 citations


Journal ArticleDOI
TL;DR: In this paper, the onset of light absorption of various Q-CdS samples (materials of extremely small particle size showing size quantization effects) was determined to obtain the dependence of Λthreshold as a function of particle radius R.

280 citations


Journal ArticleDOI
TL;DR: This paper provides a rigorous treatment of Branching structures, alias topological tree structures, and continues previous work of Colonius and Schulze on H-structures by extensive use of the so-called neighbors relation associated with a dissimilarity index.

277 citations


Journal ArticleDOI
TL;DR: In this article, a non-relativistic meson model is proposed for the description of the heavy and light vector and pseudo-scalar mesons, which yields a complete nonet below 1 GeV.
Abstract: A unitarized non-relativistic meson model which is successful for the description of the heavy and light vector and pseudo-scalar mesons yields in its extension to the scalar mesons for the same model parameters a complete nonet below 1 GeV. In the unitarization scheme real and virtual meson meson decay channels are coupled to the quark antiquark confinement channels. The flavor dependent harmonic oscillator confining potential itself has bound states ɛ(1.3 GeV),S(1.5 GeV), δ(1.3 GeV), κ(1.4 GeV), similar to the results of other bound stateq $$\bar q$$ models. However, the full coupled channel equations show poles at ɛ(0.5 GeV),S(0.99 GeV), δ(0.97 GeV), κ(0.73 GeV). Not only these pole positions can be calculated in our model also cross sections and phase shifts in the meson scattering channels which are in reasonable agreement with the available data for ππ, ηπ andKπ inS-wave scattering.

270 citations


Book ChapterDOI
Peter Jutzi1
TL;DR: In this paper, the authors discuss the π complexes of all main-group elements, including their synthesis, structure, and bonding and the literature up to 1985, up to the present day.
Abstract: Publisher Summary This chapter discusses the π complexes of all main-group elements, including their synthesis, structure, and bonding and the literature up to 1985. Compounds described have been characterized by X-ray or electron diffraction or at least by conclusive infrared (IR) or nuclear magnetic resonance (NMR) data. The term “π complex” is connected with compounds in which π ligands are polyhapto bonded to a transition metal. Many examples of the interaction between lithium and diverse π systems are documented in the literature. There are many examples known of π bonding between the heavier alkali metals and carbanionic fragments. There is no example in the literature of a stable alkene (or alkyne) complex with magnesium as central atom. Many compounds of the heavier alkaline–earth metals with organic ligands are described in the literature, for which from spectroscopic data π-interactions can be anticipated. π complexation is believed to be involved in the first step of the hydroboration of alkenes and alkynes; rearrangement reactions of organoboranes most likely involve the intermediates of a π-complex type. Alkene or alkyne complexes are mechanistically important intermediates in hydroalumination and carboalumination reactions. Using the isolobal relationship between CH or CH 2 units and corresponding transition metal or main-group element fragments, the majority of the nonclassical carbocations can be theoretically treated as π complexes.

163 citations


Journal ArticleDOI
TL;DR: In this article, the metastable decomposition of sputtered, mass-selected, cluster ions was investigated under ultrahigh-vacuum conditions, and the decay rates of cluster ion mass spectra were shown to be in agreement with calculations presented by Klots.
Abstract: The metastable decomposition of sputtered, mass-selected, cluster ions is investigated under ultrahigh-vacuum conditions. Highly excited $\mathrm{Al}_{n}^{}{}_{}{}^{+}$ and $\mathrm{Cu}_{n}^{}{}_{}{}^{+}$ cluster ions are found to decompose mainly by evaporation of single neutral atoms, whereas for $\mathrm{Si}_{n}^{}{}_{}{}^{+}$ clusters, fission is also observed. The decay rates of $\mathrm{Cu}_{n}^{}{}_{}{}^{+}$ clusters are in agreement with calculations presented by Klots. Some consequences of our results for the interpretation of cluster-ion mass spectra produced by other experimental methods are discussed.

148 citations


Journal ArticleDOI
TL;DR: A basically new structure of quasi-Landau resonances is discovered with the magnetized hydrogen atom around the ionization threshold, theoretically rationalized by classical trajectory calculation.
Abstract: A basically new structure of quasi-Landau resonances is discovered with the magnetized hydrogen atom around the ionization threshold. The resonances are theoretically rationalized by classical trajectory calculation. In energy spacing and corresponding resonance time they form a highly regularly organized series with, classically, an infinite number of members.

136 citations


Journal ArticleDOI
TL;DR: Cross sections for both processes for incident-positron energies ranging from the respective thresholds to 1000 eV are determined and the positronium-formation cross section lies above all theoretical predictions.
Abstract: Positrons ionize helium atoms either by impact ionization, resulting in three outgoing particles, or by positronium formation. We determined cross sections for both processes for incident-positron energies ranging from the respective thresholds to 1000 eV. The cross section for impact ionization by positrons (${\ensuremath{\sigma}}_{\mathrm{ion}}^{+}$) exceeds the corresponding electron cross section (${\ensuremath{\sigma}}_{\mathrm{ion}}^{\ensuremath{-}}$) below 500 eV. On the high-energy side of its maximum, the positronium-formation cross section (${\ensuremath{\sigma}}_{\mathrm{Ps}}$) lies above all theoretical predictions.

132 citations


Journal ArticleDOI
TL;DR: A method is presented to solve the real algebraic Riccati equation - XNX + XA + A^{T}X + K = 0, where K = K T and N = N T .
Abstract: A method is presented to solve the real algebraic Riccati equation - XNX + XA + A^{T}X + K = 0 , where K = K^{T} and N = N^{T} . The solution for the corresponding eigenvalue problem Mx = \lambda x , where M is a Hamiltonian matrix, is computed by an algorithm similar to the QR algorithm. Special symplectic matrices are used for the transformation of M such that the Hamiltonian form is preserved during the computations.

131 citations


Journal ArticleDOI
TL;DR: It is shown by physical and genetic means that there are two megaplasmids in all strains of Rhizobium meliloti that are necessary for the effective nodulation of alfalfa.
Abstract: We have shown by physical and genetic means that there are two megaplasmids in all strains of Rhizobium meliloti that we have studied. Megaplasmids from several strains of R. meliloti were mobilized to Agrobacterium tumefaciens and to other Rhizobium strains using the Tn5-Mob system. We were also able to resolve these two megaplasmids in agarose gels for most strains, and to show that only one of them hybridized to nif and nod genes. Transfer of this plasmid, the pSym, to Agrobacterium, R. leguminosarum, and R. trifolii strains conferred on these recipients the ability to nodulate alfalfa ineffectively. The second megaplasmid did not appear to have a direct role in nodule initiation. However, we were able to complement extracellular polysaccharide (EPS-) mutants of R. meliloti by transferring this second megaplasmid into them. Furthermore, Tn5-induced EPS- mutants of R. meliloti 2011, which produced ineffective (Fix-) nodules of abnormal morphology, were shown by hybridization and complementation to carry mutations in this second megaplasmid. This demonstrates that both megaplasmids of R. meliloti are necessary for the effective nodulation of alfalfa.

122 citations


Journal ArticleDOI
A. Holle1, Gerd Wiebusch1, Jörg Main1, B. Hager1, H. Rottke1, K. H. Welge1 
TL;DR: The interest in atomic diamagnetism arises from the fact that even for the hydrogen atom with its purely Coulombic field the Schrbodinger equation is nonseparable in any coordinate system.
Abstract: Since the discovery of quasi-Landau resonances by Garton and Tomkins [1] the physics of highly excited atoms in static homogenous magnetic fields has attracted much attention [2]. Substantial progress particularly with the hydrogen atom has been achieved in recent years by theoretical [3–11] and experimental [10–14] work. The interest in atomic diamagnetism arises from the fact that even for the hydrogen atom with its purely Coulombic field the Schrbodinger equation is nonseparable in any coordinate system.

Journal ArticleDOI
TL;DR: The capacity of the arbitrarily varying channels with states sequence known to the sender is determined with the help of an elimination technique and a robustification technique, demonstrating the power of these techniques.
Abstract: The capacity of the arbitrarily varying channels with states sequence known to the sender is determined. The result is obtained with the help of an elimination technique and a robustification technique. It demonstrates once more the power of these techniques.

Journal ArticleDOI
TL;DR: In this article, the authors studied the use of unitary unitary similarity transformations in the QR decomposition, where S is either unitary or unitary symplectic, respectively.


Journal ArticleDOI
TL;DR: This 34 months' study was concerned with the social organization in a freely growing group of domestic guinea pigs from 8 to 24 individuals and the linear rank-order among the males was the most obvious characteristic of social structure.
Abstract: [This 34 months' study was concerned with the social organization in a freely growing group of domestic guinea pigs from 8 to 24 individuals. At low numbers (4♂♂, 4♀♀-6♂♂, 8♀♀) the linear rank-order among the males was the most obvious characteristic of social structure. The alpha male's dominance was not locality dependent. He defended all females against all males. Attaining the alpha position was the most successful male reproductive strategy within this dominance structured system. At high numbers (7♂♂, 9♀♀-12♂♂, 12♀♀) a different, more complex social organization developed. Long-lasting social relationships between individual males and females as well as spatial relationships became predominant. The individuals filled different social positions which remained stable for months. The males could be divided into three different categories: 1. 'Owners', who lived together with 1 to 7 females, mainly in non-overlapping territorial areas, and who probably reproduced with these females. Their main strategy of enlarging their number of females was to recruit juvenile previously 'unowned' females into their harems. 2. Non-owners, who were dominated by the owners, formed preferences for the owners' females and, by displaying this strategy, usually attained ownership later. 3. The lowest ranking 'omega' males who were withdrawn from most social interactions. Their status can be viewed as a bad state with alternative options missing. The change of social organization took place within one month. It is seen as a mechanism to facilitate adjustment to increasing population density. The change may be instigated when it is no longer economical for the alpha male to monopolize all females and he therefore adopts an alternative reproductive strategy to maximize his fitness. The proximate factor releasing the change, may be the increasing number of fights between the alpha and beta males observed during this period., This 34 months' study was concerned with the social organization in a freely growing group of domestic guinea pigs from 8 to 24 individuals. At low numbers (4♂♂, 4♀♀-6♂♂, 8♀♀) the linear rank-order among the males was the most obvious characteristic of social structure. The alpha male's dominance was not locality dependent. He defended all females against all males. Attaining the alpha position was the most successful male reproductive strategy within this dominance structured system. At high numbers (7♂♂, 9♀♀-12♂♂, 12♀♀) a different, more complex social organization developed. Long-lasting social relationships between individual males and females as well as spatial relationships became predominant. The individuals filled different social positions which remained stable for months. The males could be divided into three different categories: 1. 'Owners', who lived together with 1 to 7 females, mainly in non-overlapping territorial areas, and who probably reproduced with these females. Their main strategy of enlarging their number of females was to recruit juvenile previously 'unowned' females into their harems. 2. Non-owners, who were dominated by the owners, formed preferences for the owners' females and, by displaying this strategy, usually attained ownership later. 3. The lowest ranking 'omega' males who were withdrawn from most social interactions. Their status can be viewed as a bad state with alternative options missing. The change of social organization took place within one month. It is seen as a mechanism to facilitate adjustment to increasing population density. The change may be instigated when it is no longer economical for the alpha male to monopolize all females and he therefore adopts an alternative reproductive strategy to maximize his fitness. The proximate factor releasing the change, may be the increasing number of fights between the alpha and beta males observed during this period.]

Book ChapterDOI
01 Jan 1986
TL;DR: In this article, the authors combined previous results of d'Este and the authors can be combined in order to obtain a rather complete description of the derived category Db(A-mod) of a tubular algebra A.
Abstract: Tubular algebras are rather special algebras of global dimension 2 with 6,8,9 or 10 simple modules, but their module categories seem to be of wider interest. For a definition, we refer to [8]; we note that typical examples are the canonical tubular algebras, these are the canonical algebras of type (2,2,2,2), (3,3,3), (4,4,2) and (6,3,2); a description of these canonical algebras by quivers and relations will be recalled below. The aim of this note is to outline that previous results of d'Este and the authors can be combined in order to obtain a rather complete description of the derived category Db(A-mod) of a tubular algebra A. For a definition of the derived category Db(A) (of bounded complexes) over an abelian category A we refer to the original article by Verdier [9]° We will freely use the notation and terminology of [8]°

Book ChapterDOI
01 Jan 1986
TL;DR: In this paper, it is shown that our relations towards an object, a field of objects, or to reality are not determined by these realities alone, and they are also determined by the (conceptual or other) ideas we form of these realities.
Abstract: What is a text? At first glance, this question may seem curious to some. After all, we are concerned with mathematics textbooks for school here, and it would seem that one knows what a mathematical text in a textbook is, indeed, we have made that assumption throughout Chapter 4. Our relations towards an object, a field of objects, or to reality, however, are not determined by these realities alone, and they are not determined by these realities in a direct way, but indirectly by way of the (conceptual or other) ideas we form of these realities.

Journal ArticleDOI
TL;DR: In this article, a three-phase model of strongly interacting matter was considered, where each phase was treated as an ideal gas modified by a simple phenomenological interaction feature for nuclear matter, taking into account the baryonic repulsion.
Abstract: We consider a three-phase model of strongly interacting matter, treating each phase as an ideal gas modified by a simple phenomenological interaction feature For nuclear matter, we take into account the baryonic repulsion; for the quark-gluon plasma, we include the bag pressure; the constituent quark phase has a non-zero effective quark mass as well as an independent bag pressure By studying which phase dominates thermodynamically in what region of temperature and baryon number density, we obtain a phase diagram for strongly interacting matter and gain some insight on the relation between deconfinement and chiral symmetry restoration

Journal ArticleDOI
TL;DR: In this article, the authors introduce a set of axioms for a new class of set systems called metroids, and show that these and other essential properties of the set systems associated with metric vector spaces hold in metroids generally.

Journal ArticleDOI
TL;DR: The development of the visual system parallels the development of visual performance of the birds and delayed growth of song control nuclei coincides with development of song.
Abstract: The postnatal development of two visual areas (nucleus rotundus and ectostriatum) and two song control areas (hyperstriatum ventrale pars caudale, HVc, and nucleus robustus archistriatalis, RA) of the zebra finch brain was followed from birth to adulthood. The following parameters were investigated: (1) neuron size, (2) volume of the brain nuclei, and (3) myelination of axons. The nucleus rotundus, the diencephalic station of the tectofugal pathway, exhibits the fastest development: rotundal neurons reach their maximum size at 20 days of age; the volume of this structure reaches adult size at the same time. The process of myelination begins between day 5 and day 10 and is completed at 40 days of age. A similar temporal sequence of development is seen in the ectostriatum, except myelination starts some days later. Thus the development of these visual areas is completed at 40 days. In, contrast, the development of the song control nuclei is delayed. Neurons in RA and HVc grow steadily up to 40 days of age, attaining a size larger than that observed in adults. Whereas the volume of HVc increases until day 40 and remains stable thereafter, RA volume increases until day 70 and evidences a decrease thereafter. It is not until postnatal day 20 (RA) and day 40 (HVc) that the myelination process starts in the song control areas. Adult myelin density is achieved by 70 days in RA and by 100 days in HVc. It can be demonstrated that the development of the visual system parallels the development of visual performance of the birds. Delayed growth of song control nuclei coincides with development of song.

Journal ArticleDOI
TL;DR: Reactions in Polar Media and Polyionic Macromolecules: Permanent and Induced Dipole Moments in Polyionics.
Abstract: VI. REACTION MoMErcr AND ELECTRIc-CI~-.MICAL MECHANISM 1. Reaction Moments from Dielectric Data 2. Permanent and Induced Dipole Moments (a) Individual dipole moments (b) Total polarization (i) Induced moment (ii) Permanent moment (c) Form factors and g-factors 3. Reaction Moment and Equilibrium Constant (a) Non-polar polarizable spheres (b) Polar non-polarizable spheres (c) Polar polarizable spheres (Onsaqer) 4. Reactions in Polar Media (a) Kirkwood-FrShlich equation (b) Ion-pair equilibria in aqueous solution 5. Induced Dipole Moments in Polyionic Macromolecules

Journal ArticleDOI
H.J. Loesch1
TL;DR: In this paper, a sliding mass model for three-center reactions is formulated, which proves to be useful to rationalize the dependence of integral reaction cross section on reagent rotation by topographic attributes of the potential energy surface (PES).

Book ChapterDOI
TL;DR: In this article, the unimolecular decomposition of metal cluster ions under UHV conditions is investigated and the time evolution of the decay allows a glimpse into the cluster formation/fragmentation process.
Abstract: Cluster ions are produced by ion bombardment of thick metal targets and mass selected in a Wien filter. The unimolecular decomposition of Al n + , Cu n + , Mo n + , W n + , and Pb n + is investigated under UHV conditions. The time evolution of the decay allows a glimpse into the cluster formation/fragmentation process. Highly excited metal cluster ions decompose mainly by evaporating single neutral atoms with rates reaching 100%. The collision induced fragmentation (CIF) of stable mass selected metal cluster ions in a low pressure Ar and O2 gas target will be compared to the unimolecular decay.

Journal ArticleDOI
TL;DR: In this paper, the exact convergence rate of subdivision algorithms for various settings of polynomial and spline curve or surface representations is investigated. But the convergence rate is not known.

Journal ArticleDOI
TL;DR: In this article, the bridged metallocenes Me2Si(Me4C5H)2 and C2H4(Me2Si (Me4c5H))2 were reported.
Abstract: Metal Complexes with Bridged Permethylated Cyclopentadienyl Ligands The preparation of the permethylated silyl-bridged dicyclopentadienyl ligands Me2Si(Me4C5H)2 (1) and C2H4(Me2Si(Me4C5H))2 (2) is reported. Reaction of dimetalated 1 with TiCl4 and ZrCl4 yielded the corresponding metallocenophane dihalides 3 and 4, while treatment of the dilithio derivative of 2 with GeCl2 · dioxane, SnCl2, and FeCl2 yielded the bridged metallocenes 5, 6, and 7.

Journal ArticleDOI
TL;DR: Following lateral line stimulation with surface waves single unit activity was recorded from the periphery, torus semicircularis, and tecturn opticum of Xenopus laevis to examine the reaction of units to varying stimulus directions.
Abstract: Following lateral line stimulation with surface waves single unit activity was recorded from the periphery, torus semicircularis, and tecturn opticum ofXenopus laevis. The reaction of units to varying stimulus directions was examined. The directional specificity (DS) was calculated on the basis of spike counts per stimulus using circular statistics. It was expressed as the length of the mean vector. Discharges of primary afferents of the ramus supraorbitalis and ramus infraorbitalis were phase locked to the stimulus to a varying degree depending on the location of the corresponding groups of neuromasts. Their DS was not better than 0.26. Lemniscal fibers, representing the ascending output of the medulla and units of the torus semicircularis reached a DS of 0.10–0.24 and 0.11–0.36 respectively. Neurons in the tectum opticum were the most sharply tuned with DS ranging between 0.81 and 0.96. The surroundings were represented by the best directions of two arrays of tectal units forming a map which is in register with the representation of the corresponding visual field of the animal.

Journal ArticleDOI
TL;DR: The hydrogen atom is a peculiar case insofar as the initial states of H(n=2), from which excitation takes place, are essentially of parabolic character at the field strengths employed in this study.
Abstract: The Stark spectroscopy of the hydrogen atom has been investigated near the ionization threshold in static homogeneous external electric fields from \ensuremath{\sim}1000 to \ensuremath{\sim}8000 V/cm with use of a two-step excitation H(n=1)+\ensuremath{\Elzxh}${\ensuremath{\omega}}_{\mathrm{vuv}\ensuremath{\rightarrow}}$H(n=2)+\ensuremath{\Elzxh}\ensuremath{\omega} $_{\mathrm{uv}\ensuremath{\rightarrow}}$${\mathrm{H}}^{\mathrm{*}}$ with vuv and uv laser radiation, independently tunable and linearly polarized either parallel (\ensuremath{\pi}) or perpendicular (\ensuremath{\sigma}) with respect to the external field. Different from other, nonhydrogenic atoms, the hydrogen atom is a peculiar case insofar as the initial states of H(n=2), from which excitation takes place, are essentially of parabolic character at the field strengths employed in this study.

Journal ArticleDOI
TL;DR: The natural gene transfer system of Agrobacterium tumefaciens is exploited to introduce a soybean heat-shock gene into the genomes of sunflower and tobacco and it is found that the gene is thermoinducibly transcribed and transcripts are faithfully initiated in transgenic plants.
Abstract: High-temperature stress or heat shock induces the vigorous synthesis of heat-shock proteins in many organisms including the higher plants. This response has been implicated in the acquisition of thermotolerance. The biological importance of a group of low-molecular-mass proteins in the response of plants is indicated by the conservation of the corresponding genes. The steady-state levels of mRNAs for these proteins shift from undetectable levels at normal temperature to about 20 000 molecules per gene in the cell after heat shock. The analysis of `run-off' transcripts from isolated soybean nuclei suggests a transcriptional control of gene expression. The DNA sequence analysis of soybean heat-shock genes revealed a conservation of promoter sequences and 5-upstream elements. A comparison of the deduced amino acid sequences of polypeptides showed a conservation of structural features in heat-shock proteins between plants and animals. The implication of a common regulatory concept in the heat-shock response makes genes belonging to this family (15-18 kDa proteins) in soybean favourable candidates for investigating thermoregulation of transcription. We have exploited the natural gene transfer system of Agrobacterium tumefaciens to introduce a soybean heat-shock gene into the genomes of sunflower and tobacco. The gene is thermoinducibly transcribed and transcripts are faithfully initiated in transgenic plants. Experiments are in progress to define the regulatory sequences 5-upstream from the gene. The expression of heat-shock genes in a heterologous genetic background also provides the basis for studying the function of the proteins and their possible role in thermoprotection.

Journal ArticleDOI
TL;DR: The hypothesis that the trHP is the only effective feedback transducer for the coxo-trochanteral control loop (Schmitz 1984, 1986) is confirmed by the nerve recordings from nerve C2, and the frequency responses of the excitatory depressor motoneurones show that the spontaneous activity of the SDTr mot oneurone is modulated by the stimulus over a wide range of stimulus frequencies up to 100 Hz.
Abstract: The innervation pattern of the coxal part of the depressor trochanteris muscle is described. This muscle is located inside the coxa cavity and is innervated by motoneurones contained in nerve C2. Serial sections of nerve C2 reveal that nerve C2 contains 3 large neurones (8, 5, and 3 μm in diameter) in addition to many small neurones. In extracellular nerve recordings from nerve C2 3 large spikes could be recorded, which can easily be classified according to their amplitudes. Combined intracellular muscle recordings and extracellular nerve recordings revealed the physiological characteristics of these motoneurones, which are referred to here as the “fast depressor trochanteris” (FDTr) motoneurone and the spontaneously active “slow depressor trochanteris” (SDTr) motoneurone. The third motoneurone could be identified as an inhibitory motoneurone. Because this motoneurone was also found in nerves nl2, nl3, nl5 and in nerve C1 (to the levator trochanteris muscle) it is referred to here as the “common inhibitor” (CI) motoneurone.

Journal ArticleDOI
TL;DR: In this article, it was shown that the intermediate ion/neutral complex is not of major importance for the rate of the fragmentation of ions with high internal energies? which react in the ion source of a inass spectrometer, which follows from the current theories of ion/molecule reactions.
Abstract: Ions a, and a, corresponding to protonated p- and m-methoxymethylbenzaldehydes have been generated in a mass spectrometer by electron impact fragmentation of the correspondingly substituted l-phenylethanols (1 and 2). Metastable ions a, and urn (2nd FFR of a VG-ZAB-2F mass spectrometer) react by elimination of CH,OH, loss of HCOOCH3, formation of ions CHp=OCH3 and to a small extent by loss of CH,O and CH30CH,, respectively. The mechanisms of these reactions have been studied by extensive D-labelling, and it is shown that these fragmentations are initiated hy a transfer of the proton located originally at the carbonyl group onto the aromatic ring. The formation of ions CHp=6CH3 and the loss of CH30H occurs via n-and a-complexes. The elimination of HCOOCH, from ions up and a, corresponds to a functional group interaction between distal side chains and occurs via intermediate ion/molecule complexes formed by a protolytic cleavage of the formyl group. The loss of CHzO and CH,OCH, proceeds also by intermediate ion/molecule complexes which are generated by a protolytic cleavage of the methoxymethyl side chain in ions a, and a,. Ion/neutral complexes are intermediates during the unimolecular fragmentation reactions of isolated ions in the gas phase. This has first been noted by P. Longevialle and coworkers’ during a study of the mass spectra of certain diamino steroids and related substances. More recently, T. H. Morton has shown in a review’ that intermediate iodneutral complexes are much more important for mass spectrometric fragmentations than hitherto expected. In fact, an ion/neutral complex in which the ion and the departing neutral fragment interact by ion/dipole and ion/induced dipole forces has to be an intermediate for every fragmentation reaction. This follows from the current theories of ion/molecule reactions3 which assume the formation of an encounter complex via a loose transition state as a first reaction step. The reaction comes to completion within the complex by crossing an intrinsic energy barrier which corresponds to the ‘chemical’ transition state of bond formation and bond rearrangements. The unimolecular fragmentation of a large ion corresponds to the reversal of an association reaction of a smaller ion and the neutral fragment. Thus, by the principle of microscopic reversibility a loosely bound ion/neutral complex is passed during the fragmentation reaction after the ‘chemical’ transition state. However, this second transition state for the dissociation of the ionheutral complex is a very loose one and, thus, does not correspond to a ‘bottle neck’3 for the total reaction. Hence, the intermediate ion/neutral complex is not of major importance for the rate of the fragmentation of ions with high internal energies? which react in the ion source of a inass spectrometer,