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  • Articles  (7)
  • 1995-1999  (5)
  • 1960-1964  (2)
  • 1997  (5)
  • 1962  (2)
  • Chemistry and Pharmacology  (7)
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  • Articles  (7)
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  • 1995-1999  (5)
  • 1960-1964  (2)
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  • 1
    ISSN: 1520-5126
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The jet-cooled B˜ 1B2–X˜ 1A1 spectrum of silylidene, the simplest unsaturated silylene, has been observed for the first time. H2C=Si and D2C=Si have been produced by an electric discharge through tetramethylsilane and tetramethylsilane-d12 vapor diluted in argon at the exit of a supersonic expansion. Rotational analysis of the 000 bands yielded the following substitution structures: rs″(CSi)=1.706(5) Å, rs″(CH)=1.099(3) Å, θs″(HCH)=114.4(2)°, rs′(CSi)=1.815(5) Å, rs′(CH)=1.073(4) Å, and θs′(HCH)=133.7(1)°. The electronic transition consists primarily of strong electronically allowed perpendicular bands, but a weaker system of vibronically induced parallel bands has also been assigned. Transitions involving Δv=2 changes in the ν6 (b2) mode show up prominently in the spectrum, due to a very large change in the vibrational frequency on excitation. Silylidene has very interesting excited state decay dynamics. Anomalous S2−S0 fluorescence is observed due to the very large S2−S1 energy gap. Rotational level specific intensity anomalies are found in the laser induced fluorescence spectra. Collision-free fluorescence decay curves exhibit superimposed quantum beats for almost all the accessible rotational levels in the 000 bands of H2CSi and D2CSi. Density of states arguments lead to the conclusion that most of the beat patterns are due to coupling with high vibrational levels of the ground state, although two examples of hyperfine splittings associated with singlet–triplet interactions have also been found. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The ground and first excited singlet states of monochlorosilylene have been reexamined using pulsed discharge jet and laser induced fluorescence techniques. HSiCl and DSiCl have been produced by an electric discharge through SiHCl3 and SiDCl3 vapor in argon. The 000 band rotational constants of four isotopomers of HSiCl and the harmonic force fields for both states have been combined to obtain the following estimates of the equilibrium structures: r′′(SiCl)=2.067(3) Å, r′′(SiH)=1.525(5) Å, θ′′(HSiCl)=96.9(5)°, r(SiCl)=2.040(3) Å, r(SiH)=1.532(8) Å, and θ(HSiCl)=118.1(5)°. Previous anomalies in the ground-state structure and the excited-state vibrational frequencies have been resolved. The radiative lifetime of the 480–400 nm (A˜ 1A′′–X˜ 1A) band system of HSiCl has been measured to be 432±20 ns. © 1997 American Institute of Physics.
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  • 4
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 106 (1997), S. 7479-7490 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The vibrational and electronic spectra of hexafluorothioacetone, (CF3)2CS, a novel blue gas, have been studied. Ab initio calculations of the vibrational properties of CF3COF, CF3CSF, and (CF3)2CO were used to establish the feasibility and effectiveness of using theoretical predictions in the analysis of the spectra of perfluorinated compounds. These predictions have allowed us to obtain revised interpretations of the spectra of trifluoroacetyl fluoride and trifluorothioacetyl fluoride that are consistent with both experiment and theory and have allowed us to confirm a previous theoretical and experimental study of the spectrum of hexafluoroacetone. Similar calculations on hexafluorothioacetone predicted a ground state of C2 symmetry, with the CF3 groups staggered in an antieclipsed configuration and a pattern of vibrational frequencies similar to that of hexafluoroacetone. The gas phase and argon matrix infrared spectra and the Raman spectrum of hexafluorothioacetone were analyzed with the aid of the ab initio predictions and 20 of the 24 fundamentals were assigned. The blue color of the compound originates from very weak T1–S0 (800–675 nm) and S1–S0 (725–400 nm) transitions in the visible due to the n–π* electron promotion. Promotion of an electron from the π to the π* orbital gives rise to a very strong electronic transition in the 230–190 nm region of the ultraviolet. No emission was observed on laser excitation of hexafluorothioacetone in the visible. © 1997 American Institute of Physics.
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  • 5
    ISSN: 1520-5126
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 106 (1997), S. 4367-4375 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The jet-cooled laser induced fluorescence excitation spectrum of the A˜ 1A′′−X˜ 1A band system of DSiF has been observed using the pulsed discharge jet technique. Vibrational analysis of the spectrum yielded upper state harmonic vibrational frequencies of ω1=1322, ω2=444, and ω3=867 cm−1. Vibronic bands involving all of the upper state fundamentals of HSiF and DSiF have now been rotationally analyzed, allowing a determination of the excited state equilibrium structure as re′(SiH)=1.526±0.014 Å, re′(SiF)=1.597±0.003 Å, and θe′(HSiF)=115.0±0.6°. The harmonic frequencies and centrifugal distortion constants were used to obtain harmonic force fields and average (rz) structures for the ground and excited states. The ground state average structure was used to estimate the equilibrium structure of re″(SiH)=1.528±0.005 Å, re″(SiF)=1.603±0.003 Å, and θe″(HSiF)=96.9±0.5°. © 1997 American Institute of Physics.
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  • 7
    Electronic Resource
    Electronic Resource
    Palo Alto, Calif. : Annual Reviews
    Annual Review of Pharmacology 37 (1997), S. 339-359 
    ISSN: 0362-1642
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Medicine , Chemistry and Pharmacology
    Notes: Abstract Research on the biological roles of nitric oxide has revealed that it functions as an important signal and effector molecule in a variety of physiologic and pathologic settings. In animals, nitric oxide is synthesized enzymatically from l-arginine through the actions of the nitric oxide synthases (NOSs). The three known NOS isoforms are all dimeric, bi-domain enzymes that contain iron protoporphyrin IX, flavin adenine dinucleotide, flavin mononucleotide, and tetrahydrobiopterin as bound prosthetic groups. This chapter summarizes information regarding the structure-function aspects of the NOSs, which includes composition of the domains, the protein residues and regions involved in prosthetic group binding, catalytic properties of the domains, the relationship between dimeric structure and prosthetic group binding and function, and factors that control assembly of NOS in cells. A general model for NOS structure and assembly is presented.
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