Rotational molecular motion

Bulanin M. O., Orlova N. D. Spectroscopical investigations of molecular rotational motion in condensed media, In Spectroscopy of Interacting Molecules, ed. M. O. Bulanin, Leningrad State University, Leningrad, pp. 55-97 (1970). 

Maximizing the information entropy of a distribution gives in some sense the smoothest distribution consistent with our available information65 on this distribution. We have tested the information theory prediction of from for two different systems the Stockmayer and modified Stockmayer simulations of CO. We have already seen that these two systems represent two extreme forms of molecular rotational motion. In the Stockmayer simulation the molecules rotate essentially freely whereas in the modified Stockmayer simulation there is evidence for strongly hindered rotational motion. from the... 

As discussed in Section III, TRPAD measurements are sensitive to molecular rotational motion by virtue of their geometric dependence on the molecular axis distribution in the LF. An elegant experimental demonstration of this has been performed by Suzuki and co-workers who measured the PAD temporal evolution from excited-state pyrazine [59]. In these experiments, the origin of the Si electronic state of pyrazine was excited by a pump pulse at 323 nm, and... 

The spin-lattice relaxation times Ti due to the quadrupole interaction mechanism can be ctmverted to die rotational correlation times T2R ui a simple maimer. In the extreme narrowing limit attained by nqnd molecular rotational motions, the spin-lattice relaxation rate 1/Tj forthe m nucleus with the spin 1=1 is expressed by... 

The fluorescence intensity of quinoline derivatives has been found to increase dramatically with an increase in the molecular weight of the host polystyrene. " This is attributed to a decrease in the free volume in the polymer matrix restricting molecular rotation/motion of the fluorophore. Similar effects have been observed for juliodinemalononitrUe in different stereo-regular poly(methyl methacrylates), and temperature effects on the luminescence properties of indole and coumaric acid derivatives in different polymer matrices showed abrupt changes in emission intensity at temperatures which correspond to the onset of local relaxation processes in the polymer. ... 

Bondarenko et al., fl4) have adopted the momentum and character of the molecular rotational motion as an indication of one or the other state of aggregation. They assumed that all molecules in free internal rotation participate as a gas. This corresponds to the presence of P— and R—branches in the IR spectrum of the bands that are being investigated. From spectroscopic measurements, they concluded that above SOO C at 250 atm, the supercritical water phase was essentially gas—like. In addition, Franck and Roth (IS) have measured both the IR spectrum and Raman spectrum of water in the supercritical region. These measurements indicated limited hydrogen bonding above 400 0 with almost no bonding above 500 0 and 250 atm. 

Spin-lattice relaxation times, Tj, for water in NB-ds solutions were measured by the inversion-recovery method with the pulse sequence of (180° t 90°) . Under the extreme narrowing condition, which is realized here by the rapid molecular rotational motions, the spin-lattice relaxation rate (l/Pi) for the FI nucleus with spin 7 = 1/2 is approximately expressed by [63] ... 

The experimental evidence from diffraction indicates that solid TeFe has two solid phases, a low-temperature phase with an orientationally-ordered, base-centered monoclinic structure and C h symmetry, and a higher-temperature phase with a body-centered cubic structure and cubic Oh symmetry. The experiments with clusters of TeFs, done by electron diffraction, show both of these and at temperatures between the regions of stability of these phases, a monoclinic phase with only partial orientational order as well. Simulations of the clusters show that the transition from body-centered cubic to monoclinic involves both rotational and translational motion of the motion, while the lower-temperature transition, between monoclinic and base-centered monoclinic, requires only coupling of the molecular rotational motions.Furthermore the transition at higher temperature in clusters shows dynamic coexistence of two phases in equilibrium over a range of at least a few degrees of temperature, which immediately implies that this transition involves two local minima in the... 

The difference between the electronic and molecular rotational motions is in the radial function Rpx- In the molecular rotation motions, the radial function is assumed to be uninvolved in the quantum nature because of the typical deep potentials of interatomic bonds. However, this assumption is not appropriate for the electronic motions. Substituting Eq. (1.76) into Eq. (1.69) and (1.74) leads to the Schrodinger equation for the radial direction in polar coordinates (r, 0, [Pg.31]

In this approach, there is no explicit time dependence of the spin Hamiltonian H(t), but it is dependent on Euler angles and its change is expressed by the time evolution of Q. Hence, the spin Hamiltonian [cf. Eq. (23.8)] for systems which exhibit molecular rotational motion can be expressed by the formula ... 

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