Hydrogen rotational relaxation

Winter T. G., Hill G. L. High-temperature ultrasonic measurements of rotational relaxation in hydrogen, deuterium, nitrogen and oxygen, J. Acoust. Soc. Am. 42, 848-58 (1967). 

The rotational relaxation of low-viscosity solvents takes place in times of ps. This can be observed through time-resolved spectroscopy when the dipole moment of the excited molecule differs substantially from that of the ground state species. Table 8.2 gives a few values of these relaxation times the alcohols show rather slow relaxation because of the hydrogen bonds which associate the solvent molecules. 

In this case, as with all other hydrogen halide lasers, only P branch transitions are observed, indicating that only partial inversion is attained. The vibrational transitions observed are 1 - 0 and 2 -+ 1. There is a definite threshold flash energy, below which no laser action is observed because the chain decomposition is not fast enough. The development in time of the emission spectrum was observed and discussed in terms of rotational relaxation. 

Fig. 30. Comparison of ESR and enzyme activity changes with hydration. Effect of hydration on lysozyme dynamic properties. (Curve f) Log rate of peptide hydrogen exchange. (Curve g) , Enzyme activity (log uo) O, rotational relaxation time (log t ) of the ESR probe TEMPONE. From Rupley et al. (1983).

This polycation was used as a model for polylysine, especially to study its behavior in acid solution. Since it has a vinyl and not a polyamide backbone, it should not adsorb hydrogen ions in acid solution and thus should not show any changes in intrinsic viscosity, transition temperature, or rotational relaxation time in acid solution. The pK° is 9.4, but because of nearest neighbor interactions, the molecule is not completely charged until pH 4 to 5 in 0.1 to l.OAf NaCl (39, 40)- The data in Table V show... 

The structure of the first solvation shell of [MMIM]+, expressed in terms of anion-cation site-site distributions, agreed very well with those reported in Ref [21]. Again, chlorides appeared located around the imidazolium C-H bonds showing the strongest association with the unique hydrogen. However, it was observed that cation-cation distribution functions did not converge well within the time scale of the simulations. That was expected given from the slow rotational relaxation of [MMIM]+, and of course the observation is also valid for the results of Ref [21]. 

The rotational relaxation of water molecules is often discussed in terms of angular momentum autocorrelation functions (e g., Stillinger and Rahman 1972 Yoshii et al. 1998). For a flexible water model, a slightly different approach can also be used. In order to separate the various modes of molecular librations (hindered rotations) and intramolecular vibrations, the scheme proposed by Bopp (1986) and Spohr et al. (1988) can be employed. The instantaneous velocities of the two hydrogen atoms of every water molecule in the molecular center-of-mass system are projected onto the instantaneous unit vectors i) in the direction of the corresponding OH bond (ui and U2) ... 

Mengel, M. and De Lucia, E.C., Helium and hydrogen induced rotational relaxation of H2CO observed at temperatures of the interstellar medium, Aftrcpfeys. 7., 543,271-274, 2000. 

Rotational dynamics of a fluorescent dye adsorbed at the interface provides useful information concerning the rigidity of the microenvironment of liquid-liquid interface in terms of the interfacial viscosity. The rotational relaxation time of the rhodamine B dye was studied by the time-resolved total internal reflection fluorescent anisotropy. In-plane rotational relaxation time of octadecylrhodamine B cation was evaluated under the presence or absence of a surfactant [26]. Table 2.8 shows that by adding a surfactant, the relaxation time and the interfadal viscosity increased. Anionic surfactants SDS and HDHP (hydrogen dihexadecylphosphate) were more effective in reducing the rotational motion, because of the electrostatic interaction. HDHP with double long chains hindered the interfacial rotation more [40]. 

In comparisons of muons with protons and of muonium with hydrogen atoms, pronounced quantum effects occur whenever dynamics are involved. In this way, muons have been utilized to probe a large variety of properties and materials insulators, semiconductors, metals, superconductors, insulators, gases, liquids, crystalline and amorphous solids, static and dynamic magnetic properties of all kinds, electron mobility, quantum diffusion, chemical reactivity and molecular structure and dynamics. The term adopted for the broad field of muon spin spectroscopy techniques, fiSR, emphasizes the analogy with other types of magnetic resonance for example EPR. juS represents muon spin , and R in a more general sense stands simultaneously for rotation , relaxation and resonance . 

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