The effect of substituted benzene dicarboxylic acid linkers on the optical band gap energy and magnetic coupling in manganese trimer metal organic frameworks

We have systematically studied a series of eight metal-organic frameworks (MOFs) in which the secondary building unit is a manganese trimer cluster, and the linkers are differently substituted benzene dicarboxylic acids (BDC). The optical band gap energy of the compounds vary from 2.62 eV to 3.57 eV, and theoretical studies find that different functional groups result in new states in the conduction band, which lie in the gap and lower the optical band gap energy. The optical absorption between the filled Mn 3d states and the ligands is weak due to minimal overlap of the states, and the measured optical band gap energy is due to transitions on the BDC linker. The Mn atoms in the MOFs have local moments of 5 mu B, and selected MOFs are found to be antiferromagnetic, with weak coupling between the cluster units, and paramagnetic above 10 K

Geotechnical Problems and Performance Studies - Chilla Power Scheme, Hardwar

Thin plastic clay seams existing in the upper Shivalik formations caused hazardous geotechnical problems during the construction of 144 MW capacity Chilla Power House Scheme, Hardwar, India by initiating several land slides. In addition, serious seepage problems occurred with the commissioning of the scheme. The paper describes in detail, the events of slides & seepage problems faced and the remedial measures adopted to counteract them. The data observed on the instruments installed to keep a vigil on the performance of the structure has also been analysed and discussed

The diffraction of light by sound waves of high frequency. Part II

The theory of the diffraction of light by sound waves of high frequency developed in our earlier paper is extended to the case when the light beam is incident at an angle to the sound wave-fronts, both from a geometrical point of view and an analytical one. It is found that the maxima of intensity of the diffracted light occur in directions which make definite angles, denoted by θ, with the direction of the incident light given by sin(θ+Φ) - sin Φ = ±[(nλ)/(λ∗ )], n (an integer) ≥ 0 where λ and λ∗ are the wave-lengths of the incident light and the sound waves in the medium. The relative intensity of the mth order to the nth order is given by Jm2( ν0 secΦ[(sint)/t] ) / Jn2 ( ν0 secΦ[(sint)/(t)]) where ν0=2πμL /λ,t=πL tanΦ/λ∗, Φ is the inclination of the incident beam of light to the sound waves, μ is the maximum variation of the refractive index in the medium when the sound waves are present and L secΦ is the distance of the light path in the medium. These results explain the variations of the intensity among the various orders noticed by Debye and Sears for variations of Φ in a very gratifying manner

The diffraction of light by high frequency sound waves. Part III. Doppler effect and coherence phenomena

The theory developed in part I of this series of papers has been developed in this paper to find the Doppler effects in the diffraction components of light produced by the passage of light through a medium containing (1) a progressive supersonic wave and (2) a standing supersonic wave. (1) In the case of the former the theory shows that the nth order which is inclined at an angle sin-1 (-nλ/λ∗) to the direction of the propagation of the incident light has the frequency ν-nν∗ where ν is the frequency of light, ν∗ is the frequency of sound and n is a positive or negative integer and that the nth order has the relative intensity J2n(2πμL/λ) where μ is the maximum variation of the refractive index, L is the distance between the faces of the cell of incidence and emergence and λ is the wavelength of light. (2) In the case of a standing supersonic wave; the diffraction orders could be classed into two groups, one containing the even orders and the other odd orders; any even order, say 2n, contains radiations with frequencies ν±2rν∗ where r is an integer including zero, the relative intensity of the ν±2rν∗ sub-component being J2n-r(πμL/λ) J2n+r(πμL/λ); and odd order, say 2n+1, contains radiations with frequencies ν ± 2r+1̅ν∗, the relative intensity of the ν ± 2r+1̅ν∗ sub-component being J2n-r , (πμL/λ) J2n+r+1(πμL/λ). These results satisfactorily interpret the recent results of Bar that any two odd orders or even ones partly cohere while an odd one and an even one are incoherent

The two types of X-ray reflection in crystals

The new type of X-ray reflection forming the subject of this paper was first described and an explanation of it on the basis of the quantum theory given in a series of papers published earlier this year by Raman and Nilakantan in these Proceedings and elsewhere. The present report is intended to be a self-contained theoretical exposition of the subject and incorporates the ideas already expounded in the papers by Raman and Nilakantan, as also the fuller mathematical treatment by Raman and Nath published in these Proceedings for July 1940. Recent experiments by Nilakantan with diamond completely establish the quantum theoretical explanation of the phenomenon

The diffraction of light by supersonic waves

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The dynamical theory of the diamond lattice. Part III. The diamond graphite transformation

The transformation of the diamond structure to the graphite structure is explained in terms of three elementary operations, one of which is a definite displacement of the two cubic face-centered lattices of diamond relative to one another. It is shown here that for a certain displacement of the component lattices, diamond attains maximum energy of its configuration and becomes unstable. The temperature at which diamond becomes unstable and transforms to graphite is calculated and is shown to be in good agreement with the experimental determinations. The ideas followed up here seem to be not very special to the diamond-graphite transformation itself but can have extensions for similar types of transformation of other substances

The normal vibrations of molecules having octahedral symmetry

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