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  • 1
    Electronic Resource
    Electronic Resource
    A versatile source to produce high-intensity, pulsed supersonic radical beams for crossed-beam experiments: The cyanogen radical CN(X2Σ+) as a case study (1999)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 70 (1999), S. 4185-4191 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: In our laboratory a novel and convenient technique has been developed to generate an intense pulsed cyano radical beam to be employed in crossed molecular beam experiments investigating the chemical dynamics of bimolecular reactions. CN radicals in their ground electronic state 2Σ+ are produced in situ via laser ablation of a graphite rod at 266 nm and 30 mJ output power and subsequent reaction of the ablated species with molecular nitrogen, which acts also as a seeding gas. A chopper wheel located after the ablation source and before the collision center selects a 9 μs segment of the beam. By changing the delay time between the pulsed valve and the choppper wheel, we can select a section of the pulsed CN(X2Σ+) beam choosing different velocities in the range of 900–1920 ms−1 with speed ratios from 4 to 8. A high-stability analog oscillator drives the motor of the chopper wheel (deviations less than 100 ppm of the period), and a high-precision reversible motor driver is interfaced to the rotating carbon rod. Both units are essential to ensure a stable cyanogen radical beam with velocity fluctuations of less than 3%. The high intensity of the pulsed supersonic CN beam of about 2–3×1011 cm−3 is three orders of magnitude higher than supersonic cyano radical beams employed in previous crossed molecular beams experiments. This data together with the tunable velocity range clearly demonstrate the unique power of our newly developed in situ production of a supersonic CN radical beam. This versatile concept is extendible to generate other intense, pulsed supersonic beams of highly unstable diatomic radicals, among them BC, BN, BO, BS, CS, SiC, SiN, SiO, and SiS, which are expected to play a crucial role in interstellar chemistry, chemistry in the solar system, and/or combustion processes. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1150050
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  • 2
    Electronic Resource
    Electronic Resource
    Crossed beam reaction of the cyano radical, CN(X 2Σ+), with methylacetylene, CH3CCH (X 1A1): Observation of cyanopropyne, CH3CCCN (X 1A1), and cyanoallene, H2CCCHCN (X 1A′) (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 2857-2860 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The chemical dynamics to form cyanopropyne, CH3CCCN (X 1A1), and cyanoallene, H2CCCHCN (X 1A′), via the neutral–neutral reaction of the cyano radical, CN (X 2Σ+), with methylacetylene, CH3CCH (X 1A1), is investigated under single collision conditions in a crossed molecular beam experiment at a collision energy of 24.7 kJ mol−1. The laboratory angular distribution and time-of-flight spectra of the C4H3N products are recorded at m/e=65, 64, 63, and 62. The reaction of d3-methylacetylene, CD3CCH (X 1A1), with CN radicals yields reactive scattering signal at m/e=68 and m/e=67 demonstrating that two distinct H(D) atom loss channels are open. Forward-convolution fitting of the laboratory data reveal that the reaction dynamics are indirect and governed by an initial attack of the CN radical to the π electron density of the β carbon atom of the methylacetylene molecule to form a long lived CH3CCHCN collision complex. The latter decomposes via two channels, i.e., H atom loss from the CH3 group to yield cyanoallene, and H atom loss from the acetylenic carbon atom to form cyanopropyne. The explicit identification of the CN vs H exchange channel and two distinct product isomers cyanoallene and cyanopropyne strongly suggests the title reaction as a potential route to form these isomers in dark molecular clouds, the outflow of dying carbon stars, hot molecular cores, as well as the atmosphere of hydrocarbon rich planets and satellites such as the Saturnian moon Titan. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.479567
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  • 3
    Electronic Resource
    Electronic Resource
    Crossed beam reaction of cyano radicals with hydrocarbon molecules. II. Chemical dynamics of 1-cyano-1-methylallene (CNCH3CCCH2; X 1A′) formation from reaction of CN(X 2Σ+) with dimethylacetylene CH3CCCH3 (X 1A1′) (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 7472-7479 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The reaction dynamics to form the 1-cyano-1-methylallene isomer CNCH3CCCH2 in its 1A′ ground state via the radical–closed shell reaction of the cyano radical CN(X 2Σ+) with dimethylacetylene CH3CCCH3 (X 1A1′) are unraveled in a crossed molecular beam experiment at a collision energy of 20.8 kJ mol−1 together with state-of-the-art electronic structure and Rice–Ramsperger–Kassel–Marcus (RRKM) calculations. Forward convolution fitting of the laboratory angular distribution together with the time-of-flight spectra verify that the reaction is indirect and proceeds by addition of the CN radical to the π orbital to form a cis/trans CH3CNC(Double Bond)CCH3 radical intermediate. This decomposes via a rather lose exit transition state located only 6–7 kJ mol−1 above the products to CNCH3CCCH2 and atomic hydrogen. The best fit of the center-of-mass angular distribution is forward–backward symmetric and peaks at π/2 documenting that the fragmenting intermediate holds a lifetime longer than its rotational period. Further, the hydrogen atom leaves almost perpendicular to the C5H5N plane resulting in sideways scattering. This finding, together with low frequency bending and wagging modes, strongly support our electronic structure calculations showing a H–C–C angle of about 106.5° in the exit transition state. The experimentally determined reaction exothermicity of 90±20 kJ mol−1 is consistent with the theoretical value, 80.4 kJ mol−1. Unfavorable kinematics prevent us from observing the CN versus CH3 exchange channel, even though our RRKM calculations suggest that this pathway is more important. Since the title reaction is barrierless and exothermic, and the exit transition state is well below the energy of the reactants, this process might be involved in the formation of unsaturated nitriles even in the coldest interstellar environments such as dark, molecular clouds and the saturnian satellite Titan. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.480071
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  • 4
    Electronic Resource
    Electronic Resource
    Crossed-beam reaction of carbon atoms with hydrocarbon molecules. V. Chemical dynamics of n-C4H3 formation from reaction of C(3Pj) with allene, H2CCCH2(X 1A1) (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 110 (1999), S. 10330-10344 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The crossed molecular beams technique was employed to investigate the reaction between ground state carbon atoms, C(3Pj), and allene, H2CCCH2(X 1A1), at two averaged collision energies of 19.6 and 38.8 kJ mol−1. Product angular distributions and time-of-flight spectra of C4H3 were recorded. Forward-convolution fitting of the data yields weakly polarized center-of-mass angular flux distributions isotropic at lower, but forward scattered with respect to the carbon beam at a higher collision energy. The maximum translational energy release and the angular distributions combined with ab initio and RRKM calculations are consistent with the formation of the n-C4H3 radical in its electronic ground state. The channel to the i-C4H3 isomer contributes less than 1.5%. Reaction dynamics inferred from the experimental data indicate that the carbon atom attacks the π-orbitals of the allenic carbon–carbon double bond barrierless via a loose, reactant-like transition state located at the centrifugal barrier. The initially formed cyclopropylidene derivative rotates in a plane almost perpendicular to the total angular momentum vector around its C-axis and undergoes ring opening to triplet butatriene. At higher collision energy, the butatriene complex decomposes within 0.6 ps via hydrogen emission to form the n-C4H3 isomer and atomic hydrogen through an exit transition state located 9.2 kJ mol−1 above the products. The explicit identification of the n-C4H3 radical under single collision represents a further example of a carbon–hydrogen exchange in reactions of ground state carbon atoms with unsaturated hydrocarbons. This channel opens a barrierless route to synthesize extremely reactive hydrocarbon radicals in combustion processes, interstellar chemistry, and hydrocarbon-rich atmospheres of Jupiter, Saturn, Titan, as well as Triton. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.478966
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  • 5
    Electronic Resource
    Electronic Resource
    Crossed beam reaction of cyano radicals with hydrocarbon molecules. I. Chemical dynamics of cyanobenzene (C6H5CN; X 1A1) and perdeutero cyanobenzene (C6D5CN; X 1A1) formation from reaction of CN(X 2Σ+) with benzene C6H6(X 1A1g), and d6-benzene C6D6(X 1A1g) (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 7457-7471 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The chemical reaction dynamics to form cyanobenzene C6H5CN(X 1A1), and perdeutero cyanobenzene C6D5CN(X 1A1) via the neutral–neutral reaction of the cyano radical CN(X 2Σ+), with benzene C6H6(X 1A1g) and perdeutero benzene C6D6(X 1A1g), were investigated in crossed molecular beam experiments at collision energies between 19.5 and 34.4 kJ mol−1. The laboratory angular distributions and time-of-flight spectra of the products were recorded at mass to charge ratios m/e=103–98 and 108–98, respectively. Forward-convolution fitting of our experimental data together with electronic structure calculations (B3LYP/6−311+G**) indicate that the reaction is without entrance barrier and governed by an initial attack of the CN radical on the carbon side to the aromatic π electron density of the benzene molecule to form a Cs symmetric C6H6CN(C6D6CN) complex. At all collision energies, the center-of-mass angular distributions are forward–backward symmetric and peak at π/2. This shape documents that the decomposing intermediate has a lifetime longer than its rotational period. The H/D atom is emitted almost perpendicular to the C6H5CN plane, giving preferentially sideways scattering. This experimental finding can be rationalized in light of the electronic structure calculations depicting a H–C–C angle of 101.2° in the exit transition state. The latter is found to be tight and located about 32.8 kJ mol−1 above the products. Our experimentally determined reaction exothermicity of 80–95 kJ mol−1 is in good agreement with the theoretically calculated one of 94.6 kJ mol−1. Neither the C6H6CN adduct nor the stable iso cyanobenzene isomer C6H5NC were found to contribute to the scattering signal. The experimental identification of cyanobenzene gives a strong background for the title reaction to be included with more confidence in reaction networks modeling the chemistry in dark, molecular clouds, outflow of dying carbon stars, hot molecular cores, as well as the atmosphere of hydrocarbon rich planets and satellites such as Saturn's moon Titan. This reaction might further present a barrierless route to the formation of heteropolycyclic aromatic hydrocarbons via cyanobenzene in these extraterrestrial environments as well as hydrocarbon rich flames. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.480070
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  • 6
    Electronic Resource
    Electronic Resource
    Crossed-beam reaction of carbon atoms with sulfur containing molecules. I. Chemical dynamics of thioformyl (HCS X2A′) formation from reaction of C(3Pj) with hydrogen sulfide, H2S(X1A1) (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 110 (1999), S. 2391-2403 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The reaction between ground state carbon atoms, C(3Pj), and hydrogen sulfide, H2S(X1A1), was studied at four average collision energies between 16.7 and 42.8 kJ mol−1 using the crossed molecular beam technique. The reaction dynamics were deducted from time-of-flight spectra and from laboratory angular distributions combined with ab initio calculations. These data suggest that the reaction proceeds through an addition of C(3Pj) to the sulfur atom to form a triplet CSH2 van der Waals complex. Successive H atom migration on the triplet or singlet surface forms a thiohydroxycarbene intermediate, HCSH, which decomposes through a tight exit transition state to HCS(X2A′)+H(2S1/2). At lower collision energies, a weak L-L′ coupling leads to isotropic center-of-mass angular distributions. As the collision energy rises, the angular distributions show increasing forward scattering thereby documenting that the reaction goes through an osculating HCSH complex. Identification of the HCS isomer under single collision conditions is a potential one-step pathway by which to form organo-sulfur molecules in interstellar environments during the collision of the comet Shoemaker-Levy 9 with Jupiter, and in combustion flames of sulfur containing fuels. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.477944
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  • 7
    Electronic Resource
    Electronic Resource
    Crossed beam reaction of the cyanogen radical, CN(X 2Σ+), with acetylene, C2H2(X 1Σg+): Observation of cyanoacetylene, HCCCN(X 1Σ+) (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 110 (1999), S. 7119-7122 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The chemical dynamics to cyanoacetylene, HCCCN(X 1Σ+), formation via the neutral–neutral reaction of cyanogen, CN(X 2Σ+), with acetylene, C2H2(X 1Σg+), is investigated in a crossed molecular beams experiment at a collision energy of 21.1 kJ mol−1. The laboratory angular distribution and time-of-flight spectra of the HCCCN product are recorded at m/e=51 and 50. Forward-convolution fitting of our data reveals that the reaction dynamics are governed by an initial attack of the CN radical to the π electron density of the acetylene molecule to form a HCCHCN collision complex on the 2A′ surface. The four heavy atoms are rotating in plane almost perpendicular to the total angular momentum vector J around the C axis of the complex which undergoes C–H bond rupture through a tight transition state to HCCCN and H. The H atom is emitted almost perpendicular to the HCCCN axis to yield a nearly "sideways" peaking of T(θ). The explicit identification of the cyanoacetylene reaction product represents a solid background for the title reaction to be included with more confidence in reaction networks modeling the chemistry in dark, molecular clouds, outflow of dying carbon stars, hot molecular cores, as well as the atmosphere of hydrocarbon rich planets and satellites such as the Saturnian moon Titan. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.478614
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  • 8
    Electronic Resource
    Electronic Resource
    Crossed beams reaction of atomic carbon, C(3Pj), with d6-benzene, C6D6(X 1A1g): Observation of the per-deutero-1,2-didehydro- cycloheptatrienyl radical, C7D5(X 2B2) (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 110 (1999), S. 6091-6094 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The reaction of atomic carbon, C(3Pj) with per-deutero benzene, C6D6 is investigated at an average collision energy of 32.1 kJ mol−1 using the crossed molecular beams technique combined with a universal mass spectrometric detector. Product angular distributions and time-of-flight spectra of C7D5 and C7D6 are recorded. Forward-convolution fitting of our time-of-flight data (TOFs) and laboratory angular distribution (LAB) together with high level electronic structure calculations on the singlet and triplet C7D6 potential energy surfaces are consistent with the formation of the per-deutero-1,2-didehydrocycloheptatrienyl radical, C7D5. No C7D6 adduct is found experimentally. Our investigations indicate that the carbon atom attacks the benzene molecule face without an entrance barrier to form an initial complex. This undergoes a ring opening to give triplet cycloheptatrienylidene as a C7D6 intermediate. The latter fragments without exit barrier via a C–D bond rupture to yield the per-deutero-1,2-didehydrocycloheptatrienyl isomer, C7D5, and a D atom. This barrierless route for the destruction of benzene may be involved in the synthesis of higher cyclic hydrocarbon derivatives in the interstellar medium, in outflows of dying carbon stars, in hydrocarbon-rich planetary atmospheres, as well as in oxygen-poor combustion flames. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.478514
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  • 9
    Electronic Resource
    Electronic Resource
    Biogene Suchtmittel Neue Konsumgewohnheiten bei jungen Abhängigen? (1999)
    Springer
    Der Nervenarzt 70 (1999), S. 1029-1033 
    Details
    ISSN: 1433-0407
    Keywords: Schlüsselwörter Polytoxikomanie ; Psilocybe ; Amanita ; Datura ; Biogene Suchtmittel ; Key words Multiple substance abuse ; Psilocybe ; Amanita ; Datura ; Biological drugs
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Description / Table of Contents: Summary Among young patients with multiple subsance abuse, a high level of abuse of natural products was noticed. In a rehabilitation clinic for young addicts 180 patients filled out a questionnaire regarding drugs they regulary consumed. It was discovered that the patients consumed high levels of Psilocybe, Amanita and Datura. The natural drugs of the 70's, Ayahuasco and Cactus, are now rarely seen. The toxicological basis of the frequently used biological drugs is discussed. The results imply that a specific exploration of patients with multiple substance abuse in regard to the use of biological drugs is necessary.
    Notes: Zusammenfassung Bei jungen Abhängigkeitskranken fiel der häufige mißbräuchliche Konsum von Naturprodukten auf. In einer Fragebogenaktion wurden 180 Patienten eines Rehabilitations-Zentrums für junge Abhängige zu ihren Gebrauchsgewohnheiten exploriert. Die Befragten gaben einen häufigen Konsum von Psilocybe, Amanita und Datura an. Die Naturdrogen der 70er Jahre, Ayahuasca und Kakteen, wurden kaum noch eingesetzt. Die Toxikologie der häufig genutzten biologischen Suchtmittel wird erörtert. Die Ergebnisse lassen eine gezielte Exploration von Abhängigen zum Gebrauch biogener Suchtmittel notwendig erscheinen.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s001150050534
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  • 10
    Electronic Resource
    Electronic Resource
    Paraneoplastische neurologische Syndrome¶Diagnostische und pathogenetische Bedeutung von Autoantikörpern (1999)
    Springer
    Der Nervenarzt 70 (1999), S. 688-701 
    Details
    ISSN: 1433-0407
    Keywords: Schlüsselwörter Paraneoplasie ; Hu ; Yo ; Ri ; Tr ; VGCC ; VGKC ; Amphiphysin ; Titin ; Recoverin ; Key words Paraneoplastic syndromes ; Hu ; Yo ; Ri ; Tr ; VGCC ; VGKC ; Amphiphysin ; Recoverin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Description / Table of Contents: Summary Paraneoplastic neurologic syndromes (PNS) are rare disorders of the nervous system that cannot be ascribed to metatastases or to destruction of vital systemic organs by the tumor or its treatment. Most frequently, PNS occur in association with small-cell lung, breast or ovarian carcinomas. The most frequent PNS is Lambert-Eaton myasthenic syndrome, which at the same time has the highest predictive value concerning an underlying carcinoma. PNS have been classified mostly under anatomical aspects but now are increasingly categorized according to specific antibodies. In certain neurologic syndromes (sensible and autonomic neuropathy, cerebellitis, limbic encephalitis, Opsoclonus-Myoclonus syndrome, Stiff-man syndrome, neuromyotonia, subacute amaurosis) specific autoantibodies are highly predictive for a neoplasm. Pathogenic relevance of these autoantibodies has been demonstrated only for antibodies against (1) voltage gated calcium channels (VGCC) in Lambert-Eaton myasthenic syndrome, (2) voltage gated potassium channels (VGKC) in neuromyotonia, and (3) recoverin in cancer associated retinopathy. The present article deals with the neurological symptoms of PNS, associated tumors, and the relevance of specific antibodies for the diagnosis and pathogenesis of PNS.
    Notes: Zusammenfassung Paraneoplastische neurologische Syndrome (PNS) sind seltene Erkrankungen, die in Assoziation mit einem Tumor auftreten, ohne durch diesen oder dessen Metastasen direkt verursacht zu sein. Am häufigsten treten PNS in Assoziation mit kleinzelligen Bronchial-, Mamma- und Ovarialkarzinomen auf. Den höchsten prädiktiven Wert im Hinblick auf einen zugrundeliegenden Tumor hat das Lambert-Eaton-Syndrom, welches zugleich auch das häufigste PNS ist. Neben der Einteilung unter anatomischen Gesichtspunkten gewinnt eine solche aufgrund spezifischer Antikörperbefunde zunehmend an Bedeutung. Bei bestimmten neurologischen Syndromen (sensible und autonome Polyneuropathie, Zerebellitis, limbische Enzephalitis, Opsoklonus-Myoklonus-Syndrom, Stiff-man-Syndrom, Neuromyotonie, subakute Amaurosis) hat den Nachweis entsprechender Autoantikörper einen höheren prädiktiven Wert in Hinblick auf das Vorliegen eines Tumors als die klinische Symptomatik allein. Eine pathogenetische Relevanz der Autoantikörper konnte bislang allerdings nur für das Lambert-Eaton-Syndrom (Antikörper gegen spannungsabhängige Kalziumkanäle, VGCC), die Neuromyotonie (Antikörper gegen spannungsabhängige Kaliumkanäle, VGKC) und die paraneoplastische Retinopathie (Antikörper gegen Recoverin) nachgewiesen werden. In der Übersicht werden die klinische Symptome der PNS, die assoziierten Tumoren und die Bedeutung der Antikörper für die Diagnose und Pathogenese der PNS dargestellt.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s001150050498
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