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  • 1990-1994  (5)
  • 1
    Electronic Resource
    Electronic Resource
    Radiative lifetimes and reactivity of metastable NO+(a 3Σ+,v) and O+2(a 4Πu,v) (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 95 (1991), S. 2259-2264 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The radiative lifetimes and reactivity of metastable NO+(a 3Σ+) and O+2(a 4Πu) have been investigated using a triple cell ion cyclotron resonance (ICR) spectrometer. Radiative lifetimes of (100±20) ms and (135±25) ms have been found for NO+(a 3Σ+) v≥1 and v≥0 respectively, with Ar and CO2 as monitor gases. The overall reaction rate of NO+(a 3Σ+,v≥1) with Ar (6.5×10−10 cm3 s−1 ) is 1 order of magnitude larger than the rate of v=0 determined in flowing afterglows. CO2 reacts at collision rate. For O+2 the overall lifetime of v≥0, determined with Ar as monitor, is (30±6) ms in between the two values (7 and 130 ms) found by Bustamente et al. using the photodissociation technique. The possible reasons for the longer lifetimes determined in previous ICR experiments is discussed. In the absence of any ab initio calculation, the experimental results on NO+(a 3Σ+) may only be compared to values calculated using an approximated perturbation model. Unfortunately, the reliability of this model, also used in the previous studies, is very limited because of the large uncertainty on the coupling between the metastable a 3Σ+ and the perturbing radiative A 1Π states.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.460982
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Time-of-flight neutron diffraction studies on the different phases of CsOH, H2O (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 5972-5978 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Neutron diffraction studies on the two dimensional ice CsOH, H2O were performed at the High Resolution Powder Diffractometer at the spallation source ISIS in England. The structure at the highest temperature comprises an O (and H) disorder perpendicular to the O2H−3 nets as well as an H disorder along an O–O connection line within the nets. The room temperature phase comprises ordered, corrugated nets, very likely built of ordered groups of OH− and H2O. The O order disorder transition can be assigned to the phase transition at 340 K. For a deuterated sample the different behavior of the OD− and the D2O group is determined. The OD− group must be described by a model with O off the threefold axis. O–D⋅⋅⋅ O bridges of different strengths result.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459481
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Experimental investigation of vibrational radiative lifetimes: H2O+ and D2O+ ions in their ground electronic state (X 2B1) (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 101 (1994), S. 1923-1929 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Radiative lifetimes of vibrationally excited H2O+ and D2O+ ions in their ground electronic state (X 2B1) have been determined using the monitor ion technique in a triple cell ion cyclotron resonance spectrometer with Fourier transform detection. The monitor reactions are proton or deuteron transfer from H(D)2O+ to CO2 and N2O. The lifetimes are corrected for collisional deactivation and reactions with the background gases occurring during the relaxation time of the ions. N2O probes all the excited vibrational levels of H2O+ and D2O+. For H2O+ only the bending modes (0,v≥1,0) contribute to the decay curve. The corresponding overall lifetime, 26.8±3 ms, is in very good agreement with the computer simulated overall lifetime including the theoretical lifetimes of Weis et al. [J. Chem. Phys. 91, 2818 (1989)] and estimated populations of the bending vibrational levels. For D2O+, the overall lifetime of the (0,v≥1,0) bending modes, 99.5±15 ms, and the lifetime of the (1,0,0) stretching mode, 27.5±4.5 ms, are observed, also in good agreement with the computer simulated and theoretical values, respectively. For both ions the overall lifetime of the (0,v≥1,0) levels may be considered as a good approximation for the radiative lifetime of the (0,1,0) level. The overall lifetimes determined with CO2 as a monitor may be attributed to the (0,v≥4,0) bending modes: 8.1±1 ms for H2O+ and 44±12 ms for D2O+. In this case, several levels having similar populations and lifetimes contribute to the decay curve, therefore the lifetimes of the individual levels cannot be determined. The agreement with computer simulated lifetimes is an indication for the validity of the theoretical lifetimes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.467702
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    Paper (German National Licenses)
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  • 4
    Electronic Resource
    Electronic Resource
    Time-of-flight neutron diffraction study on the low temperature phases of IF7 (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 101 (1994), S. 585-593 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A neutron diffraction study on iodine heptafluoride has been performed using the high resolution powder diffractometer (HRPD) at the spallation source ISIS, England. The previously unknown structure of the low temperature phase IF7 (III) was solved. IF7 (III) crystallizes in the orthorhombic space group Pbab (No. 54), a=852.160(4) pm, b=884.096(4) pm, c=599.089(2) pm with 4 formula units per unit cell. The IF7 molecule is found to exhibit an almost perfect pentagonal bipyramid with an axial bond length of 179.5(2) pm and an average equatorial bond length of 184.9 pm. The I(Feq)5 unit is slightly puckered with puckering displacements of 2.7° for two of the five Feq atoms leading to a c2 symmetry for the molecule. Two order-disorder processes lead from the plastic phase IF7 (I) to the ordered phase IF7 (III). At the first phase transition at 150 K IF7 molecules align with respect to their Fax–I–Fax units. Within the second transition at 100 K they order with respect to their I(Feq)5 units. The latter can be grouped into two sets of five-membered rings with vertices pointing up and down the orthorhombic c axis, respectively. There is evidence suggesting a temperature dependence to this second ordering process; the amount of residual disorder is 5% at 77 K and 1.4% at 5 K.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.468167
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    Paper (German National Licenses)
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  • 5
    Electronic Resource
    Electronic Resource
    Radiative lifetimes of HBr+ and DBr+ (2Π1/2, v=0, 1) (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 101 (1994), S. 265-270 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Radiative lifetimes of HBr+ and DBr+(2Π1/2, v=0, 1) have been determined using the monitor ion technique in a triple cell ICR spectrometer with Fourier transform detection. The experimental lifetimes corresponding to the vibrational transition v=1→0 are 10.2±1 ms and 56+12−11 ms for HBr+ and DBr+, respectively. The lifetimes calculated by a coupled electron pair approximation (CEPA) method similar to the method used previously for HF+ and HCl+ are 8.8 ms for HBr+ and 35.8 ms for DBr+, in rather good agreement with the experimental results. A comparison with previous experimental and theoretical results on hydrogen halides shows a shortening of the lifetime between the neutrals and the corresponding ions and a lengthening with isotopic substitution (H by D) as well as with substitution of F by Cl or by Br. The lifetimes corresponding to spin–orbit relaxation are very long 852+621−282 ms for HBr+ and 965+546−323 ms for DBr+. They can be considered as equal within the quite large experimental uncertainty on the contribution of collisional deactivation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.468179
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    Paper (German National Licenses)
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