Karl-Ludwig Oehme

Isotropic Raman line shapes near gas–liquid critical points: The shift, width, and asymmetry of coupled and uncoupled states of fluid nitrogen

In order to improve the experimental database about the additional nonrotational broadening of vibrational line shapes observable when a simple fluid approaches its gas–liquid critical point, we improved the pioneering measurements of Clouter and Kiefte [for their own review see Phys. Rev. A 33, 2749 (1986)] on the critical behavior of the polarized Raman line of fluid nitrogen by using the isotopic mixture (14N2).975−(14N15N).025, giving special attention to the fact that the isotropic line shape of liquid N2 (ν≈2327 cm−1) is affected by intermolecular vibrational resonance couplings. Using a highest-resolution double monochromator and modern CCD detection techniques, we were able to follow the temperature dependencies of the line shape parameters (i.e., shift, width, and asymmetry) of the coupled 14N2 and, depending on the S/N ratio available, of the uncoupled 14N15N in the range 45 K≲T≲300 K with up to mK resolution (1) in the β-solid phase, (2) in the coexisting liquid and gas phases, and (3) along t...

Vibrational relaxation of liquid benzene. A temperature-dependent Raman lineshape study of the selectively deuterated molecules

Abstract The halfwidths of the symmetric CH and CD stretching modes of liquid C 6 H 6 , C 6 D 6 , sym-C 6 D 3 H 3 , p -C 6 H 2 D 4 , p -C 6 H 4 D 2 , C 6 HD 5 , and C 6 H 5 D are reported. Their temperature dependence is measured in nearly the whole liquid range. There is no coincidence with present relaxation theories.

Vibrational relaxation in liquid hydrogen and deuterium bromide—The influence of self and distinct correlation functions on the isotropic and anisotropic Raman line shape

Both, the isotropic and anisotropic Raman line shapes of orthobaric liquid hydrogen and deuterium bromide are measured at 295 K and close to the triple point (185 K). Concentration dependent studies in HBr/DBr mixtures allow an experimental separation of the resonant transfer mechanism from other line broadening mechanisms. It is found that the anisotropic spectra are nearly unaffected by isotopic dilution, whereas the isotropic ones show a blue shift and a narrowing with increasing isotopic dilution. The overall contribution of the transfer mechansim to the line broadening becomes most pronounced at the lower temperature. The results are discussed in terms of a recent Raman line shape theory of Bratos and Tarjus.

Raman line shape analysis in isotopic mixtures of liquid hydrogen and deuterium chloride

Raman scattering in liquid (and in some cases in solid) isotopic mixtures of HC1 and DC1 is analyzed to prove recent theories by Bratos and Tarjus [Phys. Rev. A 32, 2431 (1985)], Logan [Mol. Phys. 58, 97 (1986)], and Knapp [J. Chem. Phys. 81, 643 (1984)] on vibrational line broadening in liquids. The concentration and temperature dependencies of isotropic [Ji(ω)] and anisotropic [Ja(ω)] line shapes have been studied between triple point (Tt) and critical temperature (Tc). It has been found that in accordance with the Bratos–Tarjus theory, Ji (ω) is much more sensitive of isotopic composition of the liquid than Ja(ω). An analysis of the concentration dependence of the broadening parameters near Tt illustrates the importance of cross correlations between the environmental broadening and the resonant intermolecular coupling. The spectral activity of three‐particle resonant transfer also becomes significant. From the change of the maximum of Ji(ω) with isotopic dilution, which is a linear function of mole fra...

Critical Raman line shape behavior of fluid nitrogen

Isotropic Raman line shapes of simple molecular fluids exhibit critical line broadening near their respective liquid-gas critical points. In order to observe this phenomenon, it is essential that the band position of a given vibrational mode is density-dependent, and that vibrational depopulation processes negligibly contribute to line broadening. Special attention was given to the fact that the isotropic (i.e., nonrotationally broadened) line shape of liquid N2 is affected by resonant intermolecular vibrational interactions between identical oscillators. By means of the well-chosen isotopic mixture (14N2).975 - (14N15N).025, the temperature and density dependences of shift, width, and asymmetry of the resonantly coupled 14N2 and, depending on the S/N ratio available, of the resonantly uncoupled 14N15N were determined, with up to milli-Kelvin resolution, in the coexisting liquid and gas phases and along the critical isochore, using a highest-resolution double monochromator and modern charge-coupled device detection techniques. Clear evidence was found that vibrational resonance couplings are present in all dense phases studied.

The slip-model for molecular reorientation and the temperature dependence of nuclear relaxation times in neat toluene and chlorobenzene

Abstract The temperature dependence of deuterium nuclear relaxation times in selectively deuterated toluene and chlorobenzene is studied. It is shown that the temperature behaviour of molecular reorientation times can be described by the method of Pecora et al. within the limit of rotational diffusion.

Isotropic Raman line widths in binary mixtures of van der Waals liquids: A comparison between isotopically and chemically diluted states of liquid methyl iodide

To analyze vibrational depopulation and dephasing mechanisms of polyatomic liquids, the presently most comprehensive study on the dilution behavior of isotropic Raman line widths has been made. By way of example, and following early proposals of Evans and Yarwood [Adv. Mol. Relaxation Int. Processes 21, 1 (1981)], liquid methyl iodide (MeI) was chosen. The low temperature study (T=207 K) covers the detailed concentration dependencies (x) of the isotropic half‐widths (FWHH) in total 17 (of 18 possible) polarized fundamentals of CH3I and in the isotopically modified molecules CH2DI, CHD2I, and CD3I (12CD3I) (i) in chemical mixtures with xenon and (partially) CF3I and (ii) in all the six binary isotopic mixtures of the isotopic species above. Furthermore, isotopic and chemical dilutions are combined in ternary mixtures of type (CX3I)0.014−(CY3I)x−0.014−Z1−x with X, Y=H, D and Z=Xe, CF3I, where the trace CX3I has been investigated to study the modulations of the vibrational transition frequency by changes of ...

Ermittlung der anisotropen brown'schen rotation monosubstituierter diphenyle in flüssiger phase durch 13CTfl-messungen

Zusammenfassung Es werden Messungen der longitudinalen 13 C-Relaxationszeiten protonierter Kohlenstoffatome in monosubstituierten Diphenylen beschrieben. Mit Hilfe des Woessnerschen Formalismus konnten die verschiedenen T 1 -Werte als Funktion der anisotropen Brownschen Rotation dargestellt werden. Zwei Rotationsdiffusionskoeffizienten der “overall”-Bewegung wurden aus den T 1 -Werten ermittelt. Es wurde festgestellt, daβ die Anisotropie der Rotation wesentlich uber dem theoretischen, durch die Tragheitsverhaltnisse bedingten, Wert liegt. Als Ursache dafur wurde das verstarkte Wirken des “frictional effects” auf die C xy -Rotation erkannt. Die intramolekulare Rotation der Phenylgruppe konnte mit zwei verschiedenen Bewegungsmodellen bestimmt werden. Es gelang, die Rotationsbarriere dieser Bewegung unter Anwendung von T 1 -Daten von Quadrupolkernen in guter Ubereinstimmung mit quantenmechanischen Werten zu ermitteln. Die Abhangigkeit der Rotationsbarriere vom Hammettschen σ m -Parameter wurde nachgewiesen.

The internal rotation barrier of 3-chloro-diphenyl and its concentration dependence in a dipolar aprotic solvent - A 13C T1 study

Abstract The anisotropic rotation of 3-chloro-diphenyl has been analysed as a function of concentration and temperature using the Woessner model equations. The

On the validity of reorientational correlation times: Liquid hydrogen bromide as an example

Abstract Reorientational correlation times τ (2) of pure liquid HBr and DBr are determined by Raman line shape analysis and nuclear magnetic relaxation. To obtain orientational correlation functions, the Fourier transforms of the anisotropic spectra are divided by the Fourier transforms of isotropic spectra which are determined either in the neat liquid or in the isotopically diluted state. The second method, which follows a theory of Bratos and Tarjus, gives somewhat better agreement with nuclear relaxation times ( 2 D in DBr). The study covers a temperature range between 185 and 295 K.