Rama Basu

Bio: Rama Basu is an academic researcher from University of Calcutta. The author has contributed to research in topic(s): Hückel's rule & Diatomic molecule. The author has an hindex of 3, co-authored 7 publication(s) receiving 28 citation(s).

SCF CI calculation of the electronic spectra of cis and trans isomers of stilbene and azo-benzene

Abstract: SCF CI calculation has been made on cis and trans isomers of stilbene and azo-benzene. It has been shown that the electronic spectra of trans isomer should appear at a shorter wave length than the corresponding cis isomers, although the resonance theory reverses their positions. Experimentally azobenzene agrees with the conclusions of SCF theory while stilbene is better represented by the resonance theory.

Studies of charge transfer interaction of nucleotides with proflavine

Abstract: The interaction of several nucleosides with proflavine hemisulphate was investigated by absorption and fluorescence spectroscopy in solvents with different dielectric constants. In each case, the ground state charge transfer complex was formed (observed from the difference absorption spectra) and the formation constants were calculated using the Benesi-Hildebrand equation (H.A. Benesi and J.H. Hildebrand, J. Am. Chem. Soc., 71 (1949) 2703). Fluorescence spectroscopy ruled out the possibility of exciplex formation as no new band was observed. However, static quenching occurred within a limited range of acceptor to donor concentration ratio. The formation constants calculated were found to be higher than those observed by adsorption spectroscopy.

An analytical algorithm for the evaluation of two-electron integrals in diatomics: A test calculation with an elliptical basis set

Abstract: A purely analytical method designed to compute the two-electron integrals that appear in anab-initio calculation of the electronic structures of diatomic molecules using elliptical basis set is presented. Test calculations are successfully carried out on LiH molecule.

SCF CI calculation of the electronic spectra of nitroso and nitro benzene

Abstract: SCF calculation with CI has been found to give a reasonable value for the longest wavelength π-π* transition in nitroso and nitro benzene if a sufficient number of configurations are taken into considerations. The applicability of this method to the case of n-π* transition is, however, of doubtful validity. For the electron density approximation of chemical reactivity simple Huckel calculation may be good enough if the parameters are carefully chosen.

Use of the CNDO Method in Spectroscopy. III. Monosubstituted Benzenes and Pyridines

Abstract: The modified CNDO method previously reported has been applied to the calculation of a series of monosubstituted benzenes and pyridines, namely, aniline, anilinium ion, benzonitrile, nitrosobenzene, phenol, phenoxide ion, toluene, pyridinium ion, pyridine‐N‐oxide, 1‐hydroxy‐pyridinium ion, the aminopyridines, and the cyanopyridines. The calculated values of the transition energies and corresponding oscillator strengths are in good agreement with available experimental data on the electronic spectra of these compounds. An analysis of the lower‐energy excited states by means of the calculated results suggests that there is an astonishingly small amount of charge‐transfer character associated with the observed ultraviolet bands. The calculations indicate that the changes in charge densities in going from the ground state to the lowest energy π → π* excited state can be related to the Hammett σ's for the substituents.

The effects of solvation in the theoretical spectra of cationic dyes

Abstract: We present a quantum-mechanical study on the solvent effects in the structure and electronic spectra of some cationic dyes: acridine orange, proflavine, safranine, neutral red, thionine and methylene blue. The geometry optimizations were carried out with the AM1 and DFT (with B3LYP functional) methods and the theoretical spectra of the dyes under study were obtained with Zindo time-dependent methods (TD–DFT and TD–HF). The solvation methodology adopted was the integral equation formulation (IEF) version of the polarizable continuum model (PCM).

Pariser-Parr-Pople-Rechnungen an Molekülen mit Aminogruppen

Abstract: Die Ergebnisse von PPP-Rechnungen fur Cyanine, Merocyanine und Aminochinone stehen in guter Ubereinstimmung mit den experimentellen Elektronen- und Schwingungsspektren. Das Spektrum des 2,5-Diaminobenzochinons-1,4 mus als unter Substituenteneinflus langwellig verschobenes p-Benzochinonspektrum gedeutet werden. Auch die Ladungsverteilung dieses Diaminochinons unterscheidet sich nur sehr wenig von derjenigen des Chinons. Diese Ergebnisse stutzen die Zuordnung der IR-Spektren der Aminochinone von Draber und Wallenfels und zeigen, das in den Aminochinonen der Chinoncharakter so ausgepragt ist, das es unnotig erscheint, sie als Quadrupol-merocyanine zu formulieren.

Organic chemistry in Titan׳s upper atmosphere and its astrobiological consequences: I. Views towards Cassini plasma spectrometer (CAPS) and ion neutral mass spectrometer (INMS) experiments in space

Abstract: The discovery of carbocations and carbanions by Ion Neutral Mass Spectrometer (INMS) and the Cassini Plasma Spectrometer (CAPS) instruments onboard the Cassini spacecraft in Titan׳s upper atmosphere is truly amazing for astrochemists and astrobiologists. In this paper we identify the reaction mechanisms for the growth of the complex macromolecules observed by the CAPS Ion Beam Spectrometer (IBS) and Electron Spectrometer (ELS). This identification is based on a recently published paper (Ali et al., 2013. Planet. Space Sci. 87, 96) which emphasizes the role of Olah׳s nonclassical carbonium ion chemistry in the synthesis of the organic molecules observed in Titan׳s thermosphere and ionosphere by INMS. The main conclusion of that work was the demonstration of the presence of the cyclopropenyl cation – the simplest Huckel׳s aromatic molecule – and its cyclic methyl derivatives in Titan׳s atmosphere at high altitudes. In this study, we present the transition from simple aromatic molecules to the complex ortho-bridged bi- and tri-cyclic hydrocarbons, e.g., CH 2 + mono-substituted naphthalene and phenanthrene, as well as the ortho- and peri-bridged tri-cyclic aromatic ring, e.g., perinaphthenyl cation. These rings could further grow into tetra-cyclic and the higher order ring polymers in Titan׳s upper atmosphere. Contrary to the pre-Cassini observations, the nitrogen chemistry of Titan׳s upper atmosphere is found to be extremely rich. A variety of N-containing hydrocarbons including the N-heterocycles where a CH group in the polycyclic rings mentioned above is replaced by an N atom, e.g., CH 2 + substituted derivative of quinoline (benzopyridine), are found to be dominant in Titan׳s upper atmosphere. The mechanisms for the formation of complex molecular anions are discussed as well. It is proposed that many closed-shell complex carbocations after their formation first, in Titan׳s upper atmosphere, undergo the kinetics of electron recombination to form open-shell neutral radicals. These radical species subsequently might form carbanions via radiative electron attachment at low temperatures with thermal electrons. The classic example is the perinaphthenyl anion in Titan׳s upper atmosphere. Therefore, future astronomical observations of selected carbocations and corresponding carbanions are required to settle the key issue of molecular anion chemistry on Titan. Other than earth, Titan is the only planetary body in our solar system that is known to have reservoirs of permanent liquids on its surface. The synthesis of complex biomolecules either by organic catalysis of precipitated solutes “on hydrocarbon solvent” on Titan or through the solvation process indeed started in its upper atmosphere. The most notable examples in Titan׳s prebiotic atmospheric chemistry are conjugated and aromatic polycyclic molecules, N-heterocycles including the presence of imino >C N–H functional group in the carbonium chemistry. Our major conclusion in this paper is that the synthesis of organic compounds in Titan׳s upper atmosphere is a direct consequence of the chemistry of carbocations involving the ion–molecule reactions. The observations of complexity in the organic chemistry on Titan from the Cassini–Huygens mission clearly indicate that Titan is so far the only planetary object in our solar system that will most likely provide an answer to the question of the synthesis of complex biomolecules on the primitive earth and the origin of life.

The Host-Guest Chemistry of Proflavine with Cucurbit[6,7,8]urils

Abstract: The binding of the polyaromatic guest, 3,6-diaminoacridine (Proflavine) to cucurbit[n]uril (CB[n]) where n = 6, 7 and 8 has been studied by fluorescence spectrophotometry and binding constants determined using a least squares fitting method. Titration of CB[8] into a solution of Proflavine results in a 95% decrease in fluorescence up to a CB[8] to Proflavine ratio of 2:1. From the induced fluorescence spectra a binding constant of 1.9 × 107 M− 1 was determined. When Proflavine is titrated into a solution of CB[8] a similar binding constant is calculated (1.3 × 107 M− 1). Titration of CB[6] into a solution of Proflavine yields a decrease in fluorescence of 18–20%, but no binding is observed beyond what is seen within experimental error. Finally, titration of CB[7] into a solution of Proflavine results in an increase in fluorescence (32%) and a blue-shift of the emission wavelength from 509 nm to 485 nm. From the induced fluorescence spectra a binding constant of 1.65 × 107 M− 1 was determined. From 1H NMR ...