Browsing by Author "L.B. Tiwari"

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A study of the fluorescence quenching of chlorophyll by photoacoustic spectrometry
(1985) V. Upadhyaya; L.B. Tiwari; S.P. Mishra
The fluorescence quenching of chlorophyll a in acetone by chloranil, p-benzoquinone and m-dinitrobenzene has been studied using a single beam photoacoustic spectrometer. Using a modified Stern-Volmer equation the quenching constants have also been determined. © 1985.
Electret microphone for use in photoacoustic spectrometer and photoacoustic spectrum of some rare earth oxide powders
(Springer India, 1982) V.N. Rai; L.B. Tiwari; S.N. Thakur; D.K. Rai
We describe a new method for the polarization of an electret foil which has proved very convenient and yields a foil having very good performance in a microphone. The variations in the charge accumulation on the electret foil and its decay with time as well as the variation of the microphone sensitivity with different microphone parameters e.g. different thicknesses of the electret foil, different back plates and different polarization techniques has been investigated. The sensitivity of the home-made microphone is estimated as 1 mV/μbar. The working of this type of microphone and its comparison with a commercial microphone as used in a (laboratory made) single beam photoacoustic spectrometer is discussed. A brief description of the photoacoustic spectrometer including microphone biasing and the photoacoustic cell is given. The photoacoustic spectra of some rare earth oxides in the form of powders have been recorded. It is seen that the atomic levels of triplyionized rare earths which are not fluorescent appear very prominently in the photoacoustic spectrum. The spectra for terbium and praseodymium oxides do not show clear peaks probably due to the presence of different stoichiometric forms. © 1982 Indian Academy of Sciences.
Photoacoustic spectra of isometric amino and hydroxy pyridines
(1983) V.N. Pandey; L.B. Tiwari; S.N. Thakur
The photoacoustic spectra of isomeric aminopyridines and isomeric hydroxypyridines in the UV-visible region have been recorded in the powder form. These spectra have been analysed in the light of liquid phase absorption spectra. The relative intensities in the photoacoustic spectra have been interpreted in terms of the nonradiative transitions. A possible ordering of the singlet states arising from n →π* and π →π* electron promotions has also been suggested. © 1983.
Photoacoustic spectra of some biologically active metal chelates-II
(1988) L.B. Tiwari; Lallan Mishra; S.N. Thakur
The visible absorption spectra of 5-(p-sulphon atophenyl)-1,3,4-oxadiazole-2-thione (ligand) and the metal chelates derived from Mn(II), Co(II), Ni(II) and Zn(II) salts have been recorded, in the powder form, on a single beam photoacoustic spectrometer. The photoacoustic spectra give information about charge transfer and d-d transitions that could not be observed in their optical u.v.-vis spectra. © 1988.
Transition metal complexes of nicotinoyl-aminoguanidine
(1990) L. Mishra; D.S. Kushwaha; V.K. Singh; V.J. Ram; V.P. Tiwari; L.B. Tiwari
[No abstract available]