Asok K. Banerjee

Magnetic field effect on the micellar (C60)n−–pyrene+ radical-pair system

We report for the first time a magnetic field effect on radical pair recombination involving fullerene clusters in a fluorinated micelle. It is found that the rate of decay of radicals increases with increasing external magnetic field strength. The effect at high field is attributed to the g-anisotropy-induced relaxation mechanism.

TWO-PHOTON ABSORPTION SPECTRUM OF GADOLINIUM ELPASOLITE

Abstract Observations on parity-allowed direct two-photon transitions within the 4f 7 configuration of Gd 3+ ion in a centrosymmetric Cl − environment are presented. The observed spectrum allows identification of the 00 bands and determination of crystal field splittings. The integrated intensities have been compared with those for an O − environment and F − environment. The energy level calculations showed agreement with experiment.

Magnetic-field-induced intensification of a forbidden A1 → A1 transition in the trigonal Na3Pr(C4H4O5)3·2NaClO4·6H2O crystal

Abstract The mixing of states induced by a high magnetic field is exploited to intensify and locate a forbidden A 1 → A 1 transition in Na 3 Pr(C 4 H 4 O 5 ) 3 ·2NaClO 4 ·6H 2 O single crystal.

Circular dichroism spectrum of gadolinium diglycolate single crystal

Abstract One-photon absorption (OPA) and circular dichroism (CD) spectra of gadolinium diglycolate single crystal at room temperature are examined and analysed. Observed dipole strengths, rotational strengths and dissymmetry factors for 6 P J and 6 D J groups are compared with the calculated values and a satisfactory spectra-structure correlation between the observed and the simulated spectrum is achieved.

Magnetic circular dichroism in Na3Eu(C4H4O5)3·2NaClO4·6H2O

The absorption and magnetic circular dichroism (m.c.d.) of Na3Eu(C4H4O5)3·2NaClO4·6H2O single crystals have been measured at 100 K for the transitions 7F0→5D1,2˙ Transitions were observed to three levels that are doubly degenerate in the D3 site symmetry appropriate for the room-temperature crystal structure. Magnetic moments were determined as A/D for the levels 5D1(E)=–1.4, 5D2(1E)= 1.2 and 5D2(2E)=–0.09. The occurence of a crystallographic phase transition was verified. The data could not be explained using either D3, the room-temperature site symmetry, or C2, the low-temperature site symmetry, alone. Rather a combination of these two symmetries was needed.

Absorption, circular dichroism and magnetic circular dichroism spectra of Na3Pr(C4H4O5)3· 2NaClO4·6H2O

Polarized absorption, circular dichroism, Zeeman effect and magnetic circular dichroism spectroscopy have been used to study single crystals of trigonal trisodium praseodymium tris(oxydiacetate) di(sodium perchlorate) hexahydrate, Na3Pr(C4H4O5)3·2NaClO4·6H2O. Transitions between the crystal field levels of 3H4 and 1D2, 3P0,1,2 and 1I6 have been observed and assigned. The crystal undergoes an order–disorder phase transition between 300 and 77 K which lowers the lanthanide site symmetry to C2. The distortion caused by this phase transition is small and a crystal field calculation within the D3 point group gives a reasonable fit of the experimentally observed energy levels and supports the assignments of the crystal field components. The estimated values of the parameters are F2= 302, F4= 64.3, F6= 5.9, ζ= 723, A20= 150, A40=–1508, A43= 1128, A60= 617, A63= 308 and A66= 368 cm–1.

Direction-dependent circular dichroism spectra of single crystals of cubic sodium uranyl acetate

Abstract The contribution of the electric quadrupole mechanism to the chirality of optically active cubic sodium uranyl acetate single crystals has been established by measurements of the direction dependence of circular dichroism spectra. The CD bands for Σ g + →Δ g transitions are found to be direction dependent while those for Σ g + →Π g are direction-independent for light propagation k parallel to the (100) and (111) directions of the cubic cell. The contribution of the electric quadrupole mechanism to the chirality relative to that of the magnetic dipole mechanism is estimated to be about 20%.

Linear dichroism spectra of cubic sodium uranyl acetate single crystal

Abstract The anisotropy in the absorption spectra of cubic sodium uranyl acetate single crystal has been established by measurement of linear dichroism. This represents the first observation of linear dichroism in the absence of external perturbations in a cubic system. The optical anisotropy is attributed to the partial electric-quadrupolar nature of the transition. The ratio of the electricquadrupole to the electric-dipole contributions to the intensity of the 5 ∑ g + → Δ g transitions is estimated to be of the order of 10 −6 .

Low-temperature phase transition in crystals of an optically active lanthanide complex

A second-order crystalline phase transition occurs between 120 and 5 K in trisodium lanthanide tris(oxydiacetate) di(sodium perchlorate) hexahydrate single crystals, Na3Ln(C4H4O5)3·2NaClO4·6H2O. Results from optical, circular dichroism and electron paramagnetic resonance spectroscopy are used to define the low-temperature space group. The transition is from the room-temperature space group R32 to P3121 or its mirror image P3221. It lowers the site symmetry of the lanthanide from D3 to C2 and results in movement of a sodium ion off a three-fold axis.

Spin wave excitations in the pyrovanadate α − Cu 2 V 2 O 7

The pyrovanadate