• Manas Banerjee

      Articles written in Journal of Chemical Sciences

    • Change of molecular structure in the excited states: A (CNDO/2) hole-potential study on phosphine

      Manas Banerjee Sankar Prasad Bhattacharyya

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      Molecular structure of phosphine in a number of excited electronic states is studied using the method of hole-potential within the basic framework of CNDO/2 theory. Effects of including 3d-functions of phosphorus in the basis set on computed molecular geometries, transition energies and inversion barriers in the excited states have been investigated. An attempt is made to rationalise qualitatively the structural changes in the excitedstate in terms of Walsh-type correlation diagram constructed with the eigenvalues of the Fock operator in theVN-1 potential model. A simple orbital model for predicting the nature of structural changes in the excited states is proposed.

    • Substituent effect on ionisation potential in a series of related molecules: A theoretical study in a molecular orbital framework

      Md Azizul Haque S P Bhattacharyya Manas Banerjee

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      The effect of replacing the hydrogen atoms in thioformaldehyde by halogen atoms (F, Cl) on the ionisation potential of the non-bonding electron is analysed by using the Hellman-Feynman theorem, regarding the nuclear charge of the substituent as a parameter in the many-electron Hamiltonian. The trends predicted by our theory nicely agree with the relevant ionisation potentials computed either by applying Koopmans’ theorem or by the ΔESCF method. For the carbonyls, avaible experimental data indicate the reliability of our prediction.

    • The iterative hole-particle method for excited states calculation: Application to tetratomic thiocarbonyls

      Manas Banerjee Asit Kumar Chandra

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      The single configuration SCF calculation for excited states is proposed for the various differently optimized excited states. Different sets of occupied and unoccupied one-electron orbitals are obtained for the different excited states. Morokuma's model is extended to a semiempirical CNDO basis. The method predicts excited state geometry quite well. Qualitative agreement in the calculated transition energies, singlet-triplet splitting and barrier to inversion has been found and the results indicate no major deviation in the trends followed in similar non-iterative simple hole-potential calculation. As expected, convergence could not be achieved in all1ππ* calculations in the non-planar geometry. Calculations in the planar geometry, however, showed convergence with difficulty. One interesting feature is a gradual decrease in the energy difference between3ηπ* and3ππ* states with successive fluorine substitution, ultimately leading to an inversion in the order in F2CS. The prediction of3ππ* as theT1 state in F2CS is discussed in the context of photochemistry exhibited by certain aromatic carbonyl compounds. Probable extension of the present model to develop an average Fock operator for single excitations and also a one-electron operator for double excitations is proposed.

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