• R D Tewari

      Articles written in Pramana – Journal of Physics

    • 1,3(n-π*) excited states of benzaldehyde

      R D Tewari P C Mishra

      More Details Abstract Fulltext PDF

      Geometries of the first triplet and first singletn-π* excited states of benzaldehyde have been optimized using thesindo 1 molecular orbital wave-function (with CI) and the Newton-Raphson method. The triplet excited state geometry of the molecule is found to be appreciably non-planar whereas that of the singlet excited state is planar. A crossing of molecular orbitals occurs in going from the ground state equilibrium geometry to the triplet and singletn-π* excited state equilibrium geometries. Existence of the para-directing effect of the singletn-π* transition for electronic charges found in an earlier work is confirmed by the present work. The tripletn-π* excitation rearranges electronic charges mainly on the CHO group. It is found that the dipole moment of the molecule would appreciably increase following the singletn-π* excitation whereas the same would appreciably decrease following the tripletn-π* excitation.

    • Photoaddition of water to uracil: A model study of loss of absorbance by pyrimidine adducts using geometry optimization of ground and excited states

      P C Mishra R D Tewari

      More Details Abstract Fulltext PDF

      Geometries of the ground, first triplet and first singlet excited states of a hydrohydroxide of uracil have been optimized using the SINDO 1 SCF molecular orbital method in conjunction with configuration interaction. The first triplet and first singlet transitions of the molecule are found tc/be of (π-sp*) type which shows their orbitally forbidden character. Thus an explanation as to why the adducts formed by the addition of H2O, hydroxylamine, bisulphite etc at the CC double bonds of pyrimidines do not absorb in the characteristic 260 nm region has been provided.

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