• S P Bhattacharyya

Articles written in Journal of Chemical Sciences

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

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.

• On the use of dipole moment as a collective coordinate in constrained variational calculations

The dipole moment function of a diatomic molecule may be viewed as a continuous collective coordinate which encodes a lot of information about sharing of electrons between the atoms concerned. By its very nature it takes cognizance of certain many-body effects and should shape the constrained wavefunction or the one electron density in much the same way as would explicit inclusion of the same many-body effects. A case study of the problem with lithium hydride as the model system has been presented and the long range behaviour of the constrained density analysed. The spectrum of the constrained Fock operator is compared with that of the unconstrained one.

• Basicity of some proto-typical carbonyls in the ground and some low lying excited states: Application of the orthogonal gradient method of orbital optimization in an INDO-MC-SCF framework-I

Gas phase proton affinities of formaldehyde and fluoroformaldehyde in the ground,1,3* (lowest) and3ππ* (lowest) states have been theoretically studied within the framework of the INDO-MC-SCF orthogonal gradient method developed earlier. Complete geometry optimization has been carried out for both the protonated and unprotonated bases in the ground and relevant excited states. Computed proton affinities (PA) of H2CO in different electronic states are in the following order:$$PA({}^1S_0 ) &gt; PA({}^3\pi \pi ^ * ) \sim PA({}^1n\pi ^ * ) &gt; PA({}^3n\pi ^ * )$$ In F2CO, however, the ordering turns out to be different viz PA(1S0)&gt;PA(1*)&gt;PA(3*)&gt;PA(3ππ*) for protonation at the carbonyl oxygen. For protonation at the F atom the ordering is PA(1S0)&gt;PA(3*)&gt;PA(1*)&gt;PA(3ππ*). Protonation at the oxygen atom is predicted to be energetically more favourable than protonation at one of the F atoms by approximately 30 kcal/mole in all the states studied. The role of Fermi correlation in shaping the difference in proton affinities of the singlet and triplet* states of H2CO is discussed.

• Transcription of the results of quantum chemical calculations in terms of the classical notion of molecular structures: The cases of some small carbonyls in the ground and excited states

Quantum chemical valence parameters of several carbonyl molecules in the ground and excited states are calculated by invoking the INDO-orthogonal gradient method in an MC-SCF framework. These parameters are then used to construct state-specific structural descriptions of these molecules in terms of superposition of several canonical structures. Photochemical reactivities of some of these molecules are sought to be explained on the basis of the picture that emerges.

• Journal of Chemical Sciences

Volume 134, 2022
All articles
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• Editorial Note on Continuous Article Publication

Posted on July 25, 2019