Browsing by Author "M.K. Haque"

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Effect of substitution on the electronic spectra of benzaldehyde
(1979) M.K. Haque; S.N. Thakur
The effects of substitution of a ring hydrogen atom of benzaldehyde by a fluorine or chlorine atom have been explored by studying the (n, π*) triplet-singlet and singlet-singlet electronic transitions in the three isomeric fluoro- and chlorobenzaldehydes. The changes due to electronic excitation in a number of vibrational frequencies have been used to determine qualitative changes in the molecular geometry of these molecules in going from ground to excited states. © 1979.
Electronic emission spectra of o- and m-fluorobenzaldehyde vapours
(Springer India, 1981) M.K. Haque; S.N. Thakur
The high resolution nπ* electronic emission spectra of o- and m-fluoro-benzaldehyde vapours in the region 365-560 nm excited in a discharge are reported for the first time. The spectra of both the compounds consist of the A 1 A″ -X 1 A′ fluorescence as well as the a 3 A″ -X 1 A′ phosphorescence bands. In the case of o-isomer, all the eleven out-of-plane vibrations have been observed in the fluorescence and the phosphorescence, though weakly in the latter, whereas in the case of m-isomer, only ten have been observed in the fluorescence and nine in the phosphorescence. It is found that the most intense bands in both the fluorescence and the phosphorescence spectra of these molecules belong to the trans-O rotamer. © 1993 Indian Academy of Sciences.
Electronic emission spectrum of p-fluorobenzaldehyde vapour
(1978) M.K. Haque; S.N. Thakur
The high resolution electronic emission spectrum of p-fluorobenzaldehyde vapour excited in a discharge is reported for the first time. The spectrum consists of both the ã3A″-X̃1A′ phosphorescence and the Ã1A″-X̃1A′ fluorescence bands. Whereas all the eleven out-of-plane vibrations appear in the fluorescence spectrum, only the φ-CHO torsional vibration and the φ-CHO wagging vibration appear in the phosphorescence. A total of thirty ground state vibrational frequencies out of the thirty-six possible fundamentals have been obtained from the emission bands. Both the fluorescence and the phosphorescence emission spectra of p-fluorobenzaldehyde are very similar to those of benzaldehyde itself. This shows that the electronic transitions are not very sensitive to the substitution of fluorine at the para position of benzaldehyde. © 1978.
Rotational isomerism in fluoro- and chloro-benzaldehydes
(1979) M.K. Haque; S.N. Thakur
The results of the study of rotational isomerism in the nπ* electronic spectra of o- and m-substituted fluoro- and chlorobenzaldehydes are reported. It has been found that trans-O is the more stable rotamer in the ground electronic states as well as in the lowest lying singlet and triplet electronic states in all four molecules. © 1979.