• P Raghunathan

      Articles written in Journal of Chemical Sciences

    • EPR studies of phosphine photofragments in cancrinite matrix at 77K

      P Raghunathan S K Sur

      More Details Abstract Fulltext PDF

      The far-uv photolysis of phosphine sorbed in cancrinite matrix at 77 K has been studied by epr spectroscopy. Cancrinite is demonstrated to stabilise the photolytically generated radicals ·PH2, ·P and ·H. Computer simulation of the entire lineshapes has been employed to assess the spin Hamiltonian parameters for both ·PH2 and ·P. The intensity distribution pattern of the ·PH2 spectrum at 77 K is indicative of a thermally-equilibrated population of rotational states of this radical in its matrix environment. The similarity of the epr data of ·PH2 trapped in cancrinite to that isolated in rare gas matrices, as well as theisotropic nature of the31P and1H hyperfine couplings in the former situation, suggest that ·PH2 is trapped in pseudospherical cavities of cancrinite with minimal matrix perturbations. Marked departures are observed for theg- andA- values of cancrinite-trapped P atoms as compared with the gasphase counterparts.

    • NMR imaging: Mathematical modelling and spectrometer design considerations

      P Raghunathan S Krishnan K R Srivathsan

      More Details Abstract Fulltext PDF

      The mathematical modelling of ‘NMR imaging’ is presented from the electrical system design viewpoint. The response, namely, the magnetisationMxy(t), is linearly related to a system identification function made up of the nuclear spin density distribution ρ(r) and the relaxation times T1(r) and T2(r), while the r.f. excitation affects the system nonlinearly and appears as an ‘aperture’ function in the imaging equation.

      Spectrometer design considerations indicate that the resolution is limited by noise at the detection stage. In our imaging spectrometer developed for studying multiphase biospecimens, a 1 mm image resolution is feasible with a gradient of 50μT cm−1, assuming a 200 Hz frequency resolution and signal averaging.

    • Magnetic resonance lineshapes in powdered and amorphous systems

      P Raghunathan S C Sivasubramanian

      More Details Abstract Fulltext PDF

      A survey is made of the theory and applications ofEPR andNMR absorption lineshapes observed in powdered and amorphous materials. The ‘spin Hamiltonian’ and ‘resonance condition’ formalisms are reviewed, andepr andnmr lineshapes are discussed which typify the singularity characteristics in powdered materials. In the amorphous or ‘glassy’ state, the measurable spin resonance parameters often have to be viewed as being ‘randomly distributed’ according to a probability density function. Several recent probability-theory based approaches to lineshape computation for modelling the amorphous state are discussed.

    • Azido-𝑚-meconine-`high ortho’ Novolak resin-based negative photoresists for deep UV lithography

      Maneesh Sharma Anant A Naik Manoj Gaur P Raghunathan S V Eswaran

      More Details Abstract Fulltext PDF

      Photoactive chemicals blended with polymers, solvents and certain other additives serve as photoresists. A new photoactive compound (PAC), azido-𝑚-meconine absorbing in the deep UV region has been blended with `alternating’ and `semi-alternating’ and `high ortho’ alternating novolak resins, based on $m/p$-cresol. The new photoresists have been evaluated as a negative tone deep UV photoresist for mircolithography.

    • Evaluation of microlithographic performance of `deep UV’ resists: Synthesis, and 2D NMR studies on alternating `high ortho’ novolak resins

      Maneesh Sharma Anant A Naik P Raghunathan S V Eswaran

      More Details Abstract Fulltext PDF

      Lithographic evaluation of a `deep UV’ negative photoresist is discussed along with the synthesis of an alternating `high-ortho’ novolak resin. 2-D NMR studies (COSY, NOESY, HSQC, HMBC) on this resin are also discussed.

  • Journal of Chemical Sciences | News

© 2021-2022 Indian Academy of Sciences, Bengaluru.