Spectroscopic correlation for OH stretching frequency shifts of water in crystal hydrates

The shift of the uncoupled OH stretching frequency of water (from its free state position) in crystal hydrates has been plotted against a parameter r⁰ obtained by subtracting the H-bond (OH...Y) length from the sum of the free state ionic radii of O and Y. From an analysis of this curve it is inferred that MO_w coordination in hydrates reduces the ionic size of water oxygen and its effect on the OH stretching frequency is opposite to that of H-bonding.     

Tetragonal paramagnetic complex in Gd3+ doped Nd2(SO4)3·(NH4)2SO4·8H2O au]V.M. Malhotra

EPR studies of Gd³⁺ doped in single crystals of Nd₂(SO₄)₃·(NH₄)₂SO₄·8H₂O (hereafter referred to as NASO) at room (RT) and liquid nitrogen (LNT) temperatures exhibit that (1) the metal aquo complex has a tetragonal symmetry with abnormally low magnitudes of crystalline field parameters at RT and (2) NASO undergoes a possible phase transition between RT and LNT.     

Intensities of wagging and rocking bands of water in MnCl2 · 2H2O and CoCl2 · 2H2O

IR relative integrated intensities and half-widths of rocking (R) and wagging (W) bands of water in MnCl₂ · 2H₂O and CoCl₂ · 2H₂O are presented at 300 K and 120 K. Departure of observed intensity into D_W/D_R from those predicted by the fixed dipole model is attributed to anisotropic dynamic changes in dipole during these oscillations. A quantity representing the variation of this anisotropy between W and R oscillations is computed and its origin is discussed. An increase by 20% to 50% in both D_W and D_R on lowering the temperature has also been discussed.     

Structural phase transition and internal fields in rubidium thiocyanate probed through vibrational spectroscopy

A comprehensive vibrational study of Rubidium thiocyanate (RbNCS), in the 298–448°K range reveals that the orthorhombic to tetragonal transition atT _c440°K is of order-disorder type exhibiting purely second order characteristics. A consistent order-parameter exponent 0.45±0.04 has been obtained from both Raman and IR measurements. In the Raman spectra, the appearance of sidebands in both the C–N&C–S stretching modes and their temperature dependence indicate the existence and a gradual diminution of internal electric field asT approachesT _c. These results have been discussed in the context of an anharmonic oscillator model. An activation energy (U) for the reorientational motion of NCS^– ions,U0.29±0.02 eV, has been calculated from large changes in the bandwidth (_C-N) nearT _c.     

The out-of-plane vibrational modes of chlorobenzene in its ground and first singlet excited states

The study of 2699 Å electronic band system of chlorobenzene has been extended to extract out all the six b₁ and three a₂ modes in both the ground state (^eA₁) and the electronically excited first singlet state (^eB₂). The procedure of the extraction of these modes on the basis of observed sequences, cross-sequences, and overtones has especially been elaborated. Strong Fermi interaction has been observed between the vibrational level ν′_6b and combination level ν′_16a + ν′_16b in ^eB₂ state. The uniqueness of the assignments of the modes has been critically discussed.     

Integral equation formulation for buoyancy-driven convection problems

An integral equation formulation for buoyancy-driven convection problems is developed and illustrated. Buoyancy-driven convection in a bounded cylindrical geometry with a free surface is studied for a range of aspect ratios and Nusselt numbers. The critical Rayleigh number, the nature of the cellular motion, and the heat transfer enhancement are computed using linear theory. Green's functions are used to convert the linear problem into linear Fredholm integral equations. Theorems are proved which establish the properties of the eigenvalues and eigenfunctions of the linear integral operator which appears in these equations.