Library

X
feed icon rss

Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
  • 1
    Electronic Resource
    Electronic Resource
    Anisotropic molecular reorientation of liquid benzene revisited. A study using 13C magnetic relaxation through chemical shift anisotropy and spin rotation (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 3361-3365 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We report on 13C magnetic relaxation in liquid benzene (C6H6 and C6D6) at 293 K at resonance frequencies of 22.63 and 100.6 MHz. The total spin–lattice relaxation rates are separated into contributions from 13C–1H and 13C–2D dipolar, spin–rotation (SR), and chemical shift anisotropy (CSA) interactions. As the principal axis of the 13C chemical shift tensor is collinear with the sixfold axis of benzene, CSA relaxation provides information on the tumbling motion of benzene, hitherto not available from other NMR experiments. The resulting correlation time τ⊥ = 1.63 ps at 20 °C indicates a faster tumbling motion, and hence, a smaller anisotropy of benzene reorientation than usually quoted in the literature. This result is qualitatively confirmed by an analysis of 13C relaxation by SR interaction, and is in fair agreement with recent results obtained in Raman line shape measurements. It is, however, at variance with the figures deduced from Rayleigh scattering experiments. The activation energy for the tumbling motion is found to be 9.8 kJ mol−1, which is markedly larger than the activation energy of 7.7 kJ mol−1 obtained from 2D relaxation data for the motion of in-plane axes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459759
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 2
    Electronic Resource
    Electronic Resource
    Potential energy surfaces, quasiadiabatic channels, rovibrational spectra, and intramolecular dynamics of (HF)2 and its isotopomers from quantum Monte Carlo calculations (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 95 (1991), S. 28-59 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We report analytical representations of the six-dimensional potential energy hypersurface for (HF)2, the parameters of which are closely adjusted to low energy experimental properties such as hydrogen bond dissociation energy (D0=1062 cm−1 ) and vibrational–rotational spectra in the far and mid infrared. We present a detailed analysis of properties of the hypersurface in terms of its stationary points, harmonic normal mode amplitudes, and frequencies for the Cs minimum and C2h saddle point and effective Morse parameters and anharmonic overtone vibrational structure for the hydrogen bond and the HF stretching vibrations. The comparison between experimental data and the potential energy surface is carried out by means of accurate solutions of the rotational–vibrational Schrödinger equation with quantum Monte Carlo techniques, which include anharmonic interactions between all modes for the highly flexible dimer. Two extensions of the quantum Monte Carlo technique are presented, which are based on the clamped coordinate quasiadiabatic channel method and allow for the approximate calculation of excited rotational and vibrational levels.Predictions include dissociation energies D0 for isotopomers (XF)2 with X=μ, D, T (D0=477; 1169; 1217 cm−1 ). Unusual anharmonic isotope effects predicted for the out-of-plane bending fundamental ν6 [378; 276; 295; and 358 cm−1 for (HF)2, (DF)2, (HFDF), (DFHF)] can be understood in simple terms. Centrifugal effects both for the high frequency a-axis rotation and low frequency c-axis rotation are accurately calculated for the vibrational ground state and some excited states, with a best equilibrium center of mass distance Req.ab=5.14a0 between the HF monomers. A very large anharmonic interaction constant x46≈−16 cm−1 is predicted for the hydrogen bond vibration ν4 and for out-of-plane bending ν6. This leads to assignment of our earlier experimental observation of a band at 383 cm−1 as ν6+ν4−ν4(K=1←0) at almost exactly the predicted position. The fundamental ν4 is predicted at 130±10 cm−1. A new, indirect assignment of our experimental data gives ν4≈125 cm−1. Monte Carlo calculations are presented for quasiadiabatic channels and transition states for hydrogen bond dissociation. We present a discussion of symmetry correlations for these channels and symmetry effects in predissociation by rotation, nuclear spin symmetry, and parity violation. Large effects from zero point energy on the three-dimensional quantum centrifugal barriers for rotational predissociation are found. On the basis of the new data, a much improved statistical mechanical estimate for the equilibrium 2HF=(HF)2 is obtained.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.461486
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 3
    Electronic Resource
    Electronic Resource
    High resolution 1.3 μm overtone spectroscopy of HF dimer in a slit jet: Ka=0←0 and Ka=1←0 subbands of vacc=2←0 (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 97 (1992), S. 5341-5354 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Continuous wave difference frequency mixing of a single mode Nd:YAG laser at 1.06 μm and a scanning, single mode ring dye laser (R6G) in a LiNbO3 crystal generates a novel source of widely tunable near infrared radiation in the 1.2–2.2 μm region. In conjunction with the high sensitivity of a pulsed slit nozzle expansion with multipass optics (0.48 m path length), this narrow band source of tunable ir light allows the high resolution study of overtone (v=2←0) spectra for a wide variety of molecular complexes with H stretching vibrations. In this paper, we report the first rotationally resolved spectra of (HF)2 in the first HF stretching overtone region. In particular, we observe Ka=1←0 and 0←0 subbands for a vibrational state from one member of the v=2 overtone triad in (HF)2 with a band center of 7682.8228(5) cm−1. We tentatively assign this state as the hydrogen bond acceptor (i.e., free) HF stretching overtone 2νacc based on predissociation line widths and excellent agreement with predictions based on an anharmonic local mode description of (HF)2. Splittings of 0.2119(5) cm−1 (K'a = 0) and 0.0942(3) cm−1 (K'a = 1) due to interconversion tunneling are found.From the observed intensity alternation due to nuclear spin statistical weights, the overall vibrational symmetry for K'a = 0 and 1 is unambiguously determined to be Γvib=A+ and B+ for the lower and upper tunneling levels, respectively. These A+ and B+ symmetry designations correspond to irreducible representations of the MS4 molecular symmetry group, which allows for large amplitude motion and exchange of the identical HF subunits. Predissociation line broadening is observed in each of the four upper vibrational levels which varies between 56(20) and 175(25) MHz and depends sensitively on both K'a and the tunneling symmetry. This tunneling symmetry dependence, together with the unusual K'a dependence of the tunneling splitting and the anomalously large intensity ratio between the parallel and perpendicular transitions, indicates the presence of vibrational resonances in the overtone region not clearly evidenced in the analysis of the corresponding fundamental HF stretch region. Our results are discussed in the context of earlier static cell FTIR spectra and recent ab initio predictions for this overtone state. The data suggest that the overtone dynamics in (HF)2 can not be satisfactorily described as an oscillator pair connected by a 1D interconversion pathway, and may instead involve substantial coupling to other intermolecular vibrational degrees of freedom.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.463794
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 4
    Electronic Resource
    Electronic Resource
    High-resolution infrared spectroscopy of DF trimer: A cyclic ground state structure and DF stretch induced intramolecular vibrational coupling (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 98 (1993), S. 5985-5989 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present high resolution, infrared laser absorption spectra of (DF)3 in a slit supersonic jet expansion. In contrast to previous structureless near IR spectra of (HF)3, the (DF)3 data reveal clear rotational structure characteristic of a cyclic, 6-membered "ring,'' and therefore provide the first accurate experimental evidence for the equilibrium geometry of any hydrogen fluoride oligomer beyond the well-studied dimer. Furthermore, the spectra display homogeneous rotational fine structure 2–3 orders of magnitude in excess of what could be anticipated from a single vibrational band. Analysis of this fine structure elucidates a novel IVR mechanism which involves single hydrogen bond cleavage, and consequent opening of the (DF)3 ring on the 40 ps time scale.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.464860
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 5
    Electronic Resource
    Electronic Resource
    Dipole moment function and equilibrium structure of methane in an analytical, anharmonic nine-dimensional potential surface related to experimental rotational constants and transition moments by quantum Monte Carlo calculations (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 101 (1994), S. 3588-3602 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The pure rotational spectrum in the far-infrared and its absolute intensity in the vibrational ground state of CHD3 and CH3D, and the integrated band strength of the N=5 CH-stretching overtone of CHD3 in the near infrared to visible were measured by high-resolution interferometric Fourier transform techniques. The far-infrared data result in permanent electric dipole moments (||μz0||=(5.69±0.14)×10−3 D for CHD3, ||μz0||=(5.57±0.10)×10−3 D for CH3D), consistent with previous experimental data. The integrated N=5 overtone cross section is found to be (0.828±0.068) fm2. The overtone data are used, together with previous data, to derive a new, nine-dimensional, isotopically invariant dipole moment function for CH4 within the chromophore model for the CH chromophore in CHD3. With this function, the experimental data can be reproduced to an averaged factor of 1.2, in the best case. In the vibrational ground state, a nine-dimensional calculation of expectation values on a new, fully anharmonic potential surface was performed using the solution of the rovibrational Schrödinger equation by diffusion quantum Monte Carlo methods. The results for the rotational constants of several isotopomers, which include significant contributions from rovibrational interactions, indicate that the equilibrium CH bond length of methane is re=108.6 pm. The calculated value for the vibrationally averaged permanent dipole moment from these nine-dimensional vibrational quantum calculations, using the dipole moment function consistent with the analysis of the overtone bands, is μz0=−(6.6±0.4)×10−3 D for CHD3 (with positive z coordinate for the H atom) and μz0=(6.8±0.5)×10−3 D for CH3D (with positive z coordinate for the D atom) in essential agreement with the far-infrared rotational intensities. The sign could be determined unambiguously by comparison with ab initio data. We predict the permanent dipole moment of several further methane isotopomers. The polarity of the CH bond in methane is C−–H+, within our simple bond dipole model, but is discussed to be a model dependent (not purely experimental) quantity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.467544
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 6
    Electronic Resource
    Electronic Resource
    Breaking symmetry with hydrogen bonds: Vibrational predissociation and isomerization dynamics in HF–DF and DF–HF isotopomers (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 104 (1996), S. 9313-9331 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: High-resolution near-IR spectra of jet-cooled HF–DF and DF–HF isotopomers are presented and analyzed for fundamental excitation in the HF-stretching region (3870 cm−1–3960 cm−1) and DF-stretching region (2840 cm−1–2880 cm−1), based on direct absorption of tunable IR difference frequency radiation in a slit-jet supersonic expansion (10 K). Spectra are obtained for excitation of all four stretching modes, *HF–DF, HF–*DF, *DF–HF, and DF–*HF (* denotes the vibrationally excited subunit), which probe both the hydrogen/deuterium bond donor and acceptor moieties in the complex. Vibrational redshifts and predissociation broadening measurements are compared with full 6D quantum calculations on theoretical HF dimer potential surfaces, which exhibit trends in qualitatively good agreement with experiment. Each of the three DF-stretch-excited bands are fit to spectroscopic precision (Δν(approximately-less-than)0.0001 cm−1) by conventional high-resolution rotational analyses, whereas each of the four corresponding HF-stretch-excited bands appear extensively perturbed (Δν≈0.01 cm−1). This H/D isotope effect is interpreted as vibrational state mixing of the HF-stretch-excited species with a dense manifold of combination band states built on DF-stretch excitation, and therefore reflects intermolecular energy flow in the complex. Such vibrational state mixing is further corroborated by observation of "dark'' state transitions that can be tentatively assigned to *HF–DF isomer interacting with the nearly isoenergetic DF–*HF isomer. This state mixing would correspond to a vibrationally promoted "isomerization'' over the tunneling barrier, and yield a spectroscopic measure of the difference in hydrogen bond dissociation energies [ΔD0=74.7(5) cm−1] for the HF–DF and DF–HF isotopomers. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.471677
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 7
    Electronic Resource
    Electronic Resource
    On hydrogen-bonded complexes: the case of (HF)2 (1996)
    Springer
    Theoretical chemistry accounts 93 (1996), S. 61-65 
    Details
    ISSN: 1432-2234
    Keywords: Anharmonicity ; Dynamics ; Density functionals ; Infrared ; Structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The hydrogen fluoride dimer (HF)2 is the most completely characterized hydrogen bonded species incorporating a donor molecule and an acceptor molecule. We provide a summary of experimental and theoretical information pertinent to the fundamental and harmonic vibrational frequencies, equilibrium geometry and dissociation energiesD e andD 0 as well as a brief critical discussion including some new results on the potential function and current “best estimates” of experimental quantities.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01113547
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 8
    Electronic Resource
    Electronic Resource
    On hydrogen-bonded complexes: the case of (HF)2 (1996)
    Springer
    Theoretica chimica acta 93 (1996), S. 61-65 
    Details
    ISSN: 0040-5744
    Keywords: Key words: Anharmonicity ; Dynamics ; Density functionals ; Infrared ; Structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract.  The hydrogen fluoride dimer (HF)2 is the most completely characterized hydrogen bonded species incorporating a donor molecule and an acceptor molecule. We provide a summary of experimental and theoretical information pertinent to the fundamental and harmonic vibrational frequencies, equilibrium geometry and dissociation energies D e and D 0 as well as a brief critical discussion including some new results on the potential function and current “best estimates” of experimental quantities.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01113547
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 9
    Electronic Resource
    Electronic Resource
    A critical analysis of electronic density functionals for structural, energetic, dynamic, and magnetic properties of hydrogen fluoride clusters (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 18 (1997), S. 1695-1719 
    Details
    ISSN: 0192-8651
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: We present extensive computational results on density functional calculations for hydrogen fluoride species (HF)n (with 1≤n≤6) and compare them to results from other approaches and experiments, where available. Among the calculated properties we discuss equilibrium structural parameters, vibrational frequencies, electric dipole moments, IR intensities, dissociation energies, barriers for rearrangement by proton tunneling, NMR chemical shifts and spin couplings for 1H and 19F, and magnetic susceptibilities. It is found that density functional (particularly BLYP) and even more so hybrid approaches (particularly B3LYP) provide useful results. However, we show that due to some characteristic deficiencies, these are in general not competitive with more quantitative results from large basis set MP2 calculations. The calculated magnetic properties do not indicate any “aromaticity” connected to a hypothetical electronic ring current.   © 1997 John Wiley & Sons, Inc.   J Comput Chem 18: 1695-1719, 1997
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
Close ⊗
This website uses cookies and the analysis tool Matomo. More information can be found here...