Advances in Molecular Relaxation and Interaction Processes最新文献

Large scale gaussian orbital SCF-MO results are given for the title molecules, including geometry optimization. The calculated hydrogen bond lengths agree well with experiment where comparison is possible, as do the changes in electric dipole moment on complex formation. The changes in electron distribution on complex formation are discussed in terms of Mulliken population indices, and calculated hydrogen bond energies are given.

Exact results are obtained for the dynamics of short chains on the cubic lattice in the presence of excluded volume. The dynamics is used to evaluate the vector end-to-end length and squared length correlation functions. These functions are compared to those obtained by computer simulation by Kranbuehl and Verdier for longer chains. A coherent picture of the effects of excluded volume and chain length on the system properties sampled is found.

Photoreactions of 2-(2′, 4′-dinitrobenzyl)-pyridine ($\text{1}$) and 2, 2′, 4, 4′-tetranitrodiphenylmethane ($\text{2}$) were investigated by means of ps-probe beam spectroscopy. It could be shown, that the electronic ground states of aci-nitro-forms and polymethine forms of flashed compounds were populated after 50 ps (compound $\text{1}$) and 30 ps (compound $\text{2}$) direct from excited states of compounds $\text{1}$ and $\text{2}$. A possible reaction scheme will be given.

It is suggested to use the radii of inertia for the determination of ellipsoid-axes needed for the calculation of the spin-lattice-relaxation times. In addition to that the calculation of the relaxation rates will be extended for totally asymmetric ellipsoids. The recommended methods will be tested for various compounds.

Complexation effect on CH stretching vibration is investigated in R₂CHOH…Y complexes (R = CF₃, CD₃ ; Y = base) by infrared spectroscopy ; it depends on the alcohol molecular conformation. When the CH and OH bands are in the trans position, the observed down shifts of $\text{ν}$(CH) and $\text{ν}$(OH) in the complexation are linearly related ; for the gauche forms, the relation between the down shifts of $\text{ν}$(CH) and $\text{ν}$(OH) depends on R and when R = CF₃ it moreover depends on the basicity of Y. So, the directional character of the electronic displacement in H bonding is shown. No significant effect of the complexation on the integrated intensity of the ν(CH) band is observed. Solvatation of (CF₃)₂CHOH…Y by Y bases may be due to a C-H…Y hydrogen bonding.

The dielectric absorption of seven aliphatic straight chain aldehydes has been examined in a polystyrene matrix between 80 and 325 K and in the 50 to 10⁵ Hz region. For each solute two sets of absorption curves were found, one around 100 K and the other in approximately the 200 – 300 K region. The relaxation data for the 100 K region has been identified with segmental rotation and probably, with rotation about the C  CHO bond as well. The higher temperature process, which involves relaxation of appreciably larger units, may well be an overlap of molecular and larger segmental rotation. n-Nonanal was examined in a polystyrene and a polypropylene matrix and in both cases gave low and high temperaure absorption curves. The parameters for the former were almost independent of the medium whereas those for the latter process exhibited considerable variation.

Conductometric titrations of equimolar mixtures of L-glutamic acid and L-histidine indicate that these species interact more strongly than L-glutamic acid with D-histidine in dilute solution. The presence of ion pairs is confirmed by the UV spectrum of these solutions. No such stereospecific interactions were found between L-glutamic acid and L-lysine or L-ornithine. The conductometric titration curves of these compounds are identical with that of L-glutamic acid with the DL mixture of the basic amino acids.

The reorientational dynamics of an asymmetric top (a C_2v symmetry triatomic) are investigated using molecular dynamics simulation. The angular momentum autocorrelation function <$\text{J}$(t).$\text{J}$(0)>/<J²(0)> is non-exponential with a very long positive tail. The autocorrelation functions <ℓ_A(t).$\text{ol}$_A(0)>, <$\text{ol}$_B(t).$\text{ol}$_B(0)> and <$\text{ol}$_C(t).$\text{ol}$_C(0)> of three unit vectors $\text{ol}$_A, $\text{ol}$_B and $\text{ol}$_C fixed in the principle moment of inertia coordinate system are non-exponential for each of the first four Legendre polynomials P₁ to P₄.

Large-scale gaussian orbital SCF-MO results are reported for the title molecules. R_e(X…H) and D_e(X…H) values are given, and in either case the complexes OC…HF and DC…HCl are more stable than the corresponding CO…HX complexes. The changes on electronic distribution on complex formation are discussed in terms of Mulliken population indices.