P. K. Seshan

Bio: P. K. Seshan is an academic researcher from Indian Association for the Cultivation of Science. The author has contributed to research in topics: Absorption spectroscopy & Excited state. The author has an hindex of 2, co-authored 5 publications receiving 13 citations.

The absorption spectra of some aromatic compounds

Abstract: Several aromatic hydrocarbons have been studied for their absorption spectra in the vapour state over the spectral range 7000 A to 2200 A. A general analysis is made of the band systems, and the values of vibrational frequencies of the molecules in the normal and in the excited states, and of the electronic frequencies of the molecules, are calculated therefrom. These frequencies are discussed in relation to the structure of the molecules, and in relation to their physical states of aggregation.

The absorption spectra of some aromatic compounds: Part I.—Hydrocarbons

Abstract: SummarySeveral aromatic hydrocarbons have been studied for their absorption spectra in the vapour state over the spectral range 7000 Å to 2200 Å. A general analysis is made of the band systems, and the values of vibrational frequencies of the molecules in the normal and in the excited states, and of the electronic frequencies of the molecules, are calculated therefrom. These frequencies are discussed in relation to the structure of the molecules, and in relation to their physical states of aggregation.

Chemical studies on coal

Abstract: The chief constituents of wood are cellulose and lignin. It would, therefore, be natural to enquire how these two constituents are gradually destroyed in the process of coalification and to follow them up through the various stages. Doing so we find, in agreement with Dr. Mahadevan, that while both these components are being continually destroyed, their rates of destruction are very different; cellulose is destroyed very much more rapidly than lignin at the earlier stages, and more slowly than lignin at the latter stages of coalification. The relative proportion of cellulose and lignin is found to be characteristic of the stage of maturity, and thus forms a ready and very reliable index of the stage of maturity which the specimen has reached in the coalification process. The author wishes to express his grateful thanks to Prof. K. S. Krishnan for his guidance and keen interest in the progress of the work.

The absorption spectra of some aromatic compounds: Part II. Quinones and Hydroquinones

Abstract: 8. SummaryThe absorption spectra of some quinines and hydroquinones in the vapour state have been studied over a wide spectral region, from 7000 to 2200 Å, with a high dispersion spectrograph. Many of them show a vibrational structure, and some of them also a rotational fine structure. The bands for the simplest of the molecules, namely benzoquinone and hydroquinone, have been analysed, and the characteristic vibrational frequencies of the normal and excited molecules have been determined. For the other molecules the vibrational frequencies for the excited state only could be so obtained.The substances have been studied also in solution. The rotational and vibrational structures observed with the vapours are all quenched, and the maxima of absorption are considerably shifted towards the red end of the spectrum. In the solid state, in which also two of the substances were studied, there is a further shift of the absorption-maxima in the same direction.

Leishmanicidal and trypanocidal activities of Bolivian medicinal plants

Abstract: Cutaneous and mucocutaneous leishmaniasis are endemic diseases in South America, especially in the subandean areas of the humid lowlands of Bolivia. Fourteen plants used topically in folk medicine to treat cutaneous leishmaniasis were collected in the tropical regions of colonization and in the rain forest occupied by Chimane Indians. Three of four plants used by the Chimane Indians exhibited an in vitro activity against three species of Leishmania. Two of ten plants used by the colonists showed an in vitro activity. We have also included results obtained with extracts from 53 Bolivian medicinal plants used for other diseases and from 43 plants collected with basis of chemotaxonomic criteria from all parts of Bolivia. All extracts were also screened in vitro against three strains of Trypanosoma cruzi (Trypanosomatidae), the causative agent of Chagas' disease.

The Electronic Spectra of Aromatic Molecular Crystals

Abstract: Publisher Summary The chapter describes the electronic spectra of aromatic crystals.The chapter presents survey of the measured spectra to those crystals for which complete data concerning the absorption and fluorescence of crystals and solutions are available. The materials to be surveyed are benzene, hexamethylbenzene, naphthalene, anthracene, phenanthrene, durene and other derivatives of benzene and naphthalene, other aromatic hydrocarbons, other organic molecular crystals. In some cases, the principal details are presented in a strongly schematic manner in the sense that the discussion is restricted to the strongest bands or lines. In the absorption spectrum that begins in the visible or the near ultraviolet part of the spectrum, a number of electronic excitation levels are observed. These electronic levels are accompanied by the excitation levels of molecular vibrations and rotations; however, the latter can be observed only in dilute gases.

Excited Electronic Levels in Conjugated Molecules: I. Long Wavelength Ultra-Violet Absorption of Naphthalene, Anthracene and Homologs

Abstract: The method of molecular orbitals has been applied to study the long wave ultra-violet absorption of the polyacene series, naphthalene, anthracene,..... The longest wavelength in an allowed excitation probably arises from a transition between mobile electron levels of symmetry A1g → B2u, and polarized across the width of the molecule. In the first four or five members of the series, the second wavelength is due to a transition A1g → B1u, polarized along the length of the molecule. Discrepancies between this theory and both the valence-bond resonance treatment and the Lewis-Calvin theory of colour are elucidated. This assignment of transitions is in agreement with (1) calculation of absolute energies as a function of chain length, (2) calculation of relative energies of the B2u and B1u transitions, (3) limiting condition for a large number of rings, (4) calculations of intensities, and (5) some experimental work on fluorescence.