Sethu Gunasekaran | St.Peter's University (original) (raw)
Papers by Sethu Gunasekaran
Indian Journal of …, 2005
Abstract: A qualitative analysis of the enolic form of 3-oxo-L-gulofuranolactone (ascorbic acid) ... more Abstract: A qualitative analysis of the enolic form of 3-oxo-L-gulofuranolactone (ascorbic acid) has been made by a satisfactory vibrational band assignment using FTIR and FT Raman spectra. The calculated theoretical vibrational frequencies are compared with the ...
Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy, Jan 24, 2014
A new semi organic non linear optical polymeric crystal, bis (thiourea) silver (I) nitrate (TuAgN... more A new semi organic non linear optical polymeric crystal, bis (thiourea) silver (I) nitrate (TuAgN) with dimension 8×7×1.5 mm(3) has been successfully grown from aqueous solution by slow evaporation solution technique. Single crystal X-ray diffraction study reveals that the crystal belongs to orthorhombic system with non centrosymmetric space group C2221. The crystalline perfection of the crystal was analyzed by high resolution X-ray diffraction (HRXRD) rocking curve measurements. Functional groups present in the crystal were analyzed qualitatively by infrared and Confocal Raman spectral analysis. Effects due to coordination of thiourea with metal ions were also discussed. Optical absorption study on TuAgN crystal shows the minimum absorption in the entire UV-Vis region and the lower cut off wavelength of TuAgN is found to be 318 nm. Thermal analysis shows that the material is thermally stable up to 180°C. The mechanical strength and its parameters of the grown crystal were estimated...
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 2014
Melaminium bis(trifluoroacetate) trihydrate (MTFA), an organic material has been synthesized and ... more Melaminium bis(trifluoroacetate) trihydrate (MTFA), an organic material has been synthesized and single crystals of MTFA have been grown by the slow solvent evaporation method at room temperature. X-ray powder diffraction analysis confirms that MTFA crystal belongs to the monoclinic system with space group P2/c. The molecular geometry, vibrational frequencies and intensity of the vibrational bands have been interpreted with the aid of structure optimization based on density functional theory (DFT) B3LYP method with 6-311G(d,p) and 6-311++G(d,p) basis sets. The X-ray diffraction data have been compared with the data of optimized molecular structure. The theoretical results show that the crystal structure can be reproduced by optimized geometry and the vibrational frequencies show good agreement with the experimental values. The nuclear magnetic resonance (NMR) chemical shift of the molecule has been calculated by the gauge independent atomic orbital (GIAO) method and compared with experimental results. HOMO-LUMO, and other related molecular and electronic properties are calculated. The Mulliken and NBO charges have also been calculated and interpreted.
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 2009
Sanidine, a variety of feldspar minerals has been investigated through optical absorption, vibrat... more Sanidine, a variety of feldspar minerals has been investigated through optical absorption, vibrational (IR and Raman), EPR and NMR spectroscopic techniques. The principal reflections occurring at the d-spacings, 3.2892, 3.2431, 2.9022 and 2.6041 A confirm the presence of sanidine structure in the mineral. Sanidine shows five prominent characteristic infrared absorption bands in the region 1200-950, 770-720, 590-540 and 650-640 cm(-1). The Raman spectrum shows the strongest band at 512 cm(-1) characteristic of the feldspar structure, which contains four membered rings of tetrahedra. The UV-vis-NIR absorption spectrum had strong absorption features at 6757, 5780 and 5181 cm(-1) due to the combination of fundamental OH- stretching. The bands at 11236 and 8196 cm(-1)and the strong, well-defined band at (30303 cm(-1) attest the presence of Fe(2+) and Fe(3+), respectively, in the sample. The signals at g = 4.3 and 3.7 are interpreted in terms of Fe(3+) at two distinct tetrahedral positions Tl and T2 of the monoclinic crystal structure The (29)Si NMR spectrum shows two peaks at -97 and -101 ppm corresponding to T2 and T1, respectively, and one peak in (27)Al NMR for Al(IV).
Journal of Thermal Analysis and Calorimetry, 2009
Thermal decomposition behaviour of ten Indian limestones of marine origin have been studied by th... more Thermal decomposition behaviour of ten Indian limestones of marine origin have been studied by thermogravimetric (TG) and differential thermal analysis (DTA). DTA curves of limestone samples show asymmetric peak with index of shape about 0. 25. The size of calcite characteristic endothermic DTA peak remains unaffected due to the presence of impurities such as SiO2 and Al2O3. The presence sodium
Journal of Crystal Growth, 2013
ABSTRACT Single crystal of 2, 3-Dimethoxy-10-oxostrychnidinium hydrogen oxalate dihydrate has bee... more ABSTRACT Single crystal of 2, 3-Dimethoxy-10-oxostrychnidinium hydrogen oxalate dihydrate has been grown by slow evaporation solution growth technique (SEST) using ethanol-water solution at room temperature. It crystallizes in the orthorhombic system with space group of P212121. The crystalline perfection of the grown single crystal has been examined by high resolution X-ray diffraction analysis (HRXRD). The optical absorption studies show that the crystal is transparent in the visible region with a lower cut-off wavelength of 342 nm and the optical energy band gap Eg is found to be 3.52 eV. The electrical properties have been assessed by dielectric measurement at different temperatures. Hardness values measured using Vickers hardness indenter show considerable anisotropy. Laser damage threshold study is also carried out for the grown crystal.
Crystal Research and Technology, 2006
Applied Clay Science, 2008
Chrysotile, a variety of serpentine minerals has been investigated through optical absorption and... more Chrysotile, a variety of serpentine minerals has been investigated through optical absorption and EPR studies. High magnification electron micrographs have shown the existence of a tube-like structure of the layers. The optical absorption indicated the presence of Fe2+ and Fe3+ ions. The bands at 10,989, 11,111, 15,873 19,608, 22,727 and 26,316 cm−1 we assigned to Fe3+ and the other bands at
International Journal of Quantum Chemistry, 2000
Molecular Simulation, 2010
Thiourea is potentially capable of forming coordinate bonds through both sulphur and nitrogen eve... more Thiourea is potentially capable of forming coordinate bonds through both sulphur and nitrogen even though the extremely low basicity of the ligands militates against the formation of nitrogen-metal bonds. Both these possibilities will be reflected in the infrared spectra of the complexes. The centrosymmetric thiourea molecule when combined with inorganic salts yields non-centrosymmetric complexes, which has non linear optical properties. In the present study optically transparent crystals of Pure and doped BTMC crystals have been grown. The crystals are characterized by subjecting to Powder XRD, AAS, FTIR, UV and SHG tests are discussed and values tabulated.
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 2012
Chemical Physics Letters, 2003
International Journal of Quantum Chemistry, 2005
ABSTRACT Density functional calculations at the B3LYP/6-31G* level were performed for perylene te... more ABSTRACT Density functional calculations at the B3LYP/6-31G* level were performed for perylene tetracarboxylic dianhydride (PTCDA) and its potential derivatives modified by replacing the two anhydride ether groups with B-, N-, S-, and Se-containing groups, as well as for perylene monomer and dimer structures. The predicted infrared (IR) and Raman spectroscopic properties of PTCDA have been compared with the observed experimental spectra and available theoretical data. In addition, the isotope effect on the Raman and IR spectra of PTCDA by the replacement of all H atoms by deuterium isotopes, as well as the estimated UV-vis properties of PTCDA and its modified derivatives, based on the results of the time-dependent DFT method have been also presented. It was shown that the formation of polyperinaphthalene films affects strongly the predicted theoretically IR, Raman and UV-vis spectra of the precursor PTCDA. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005
Journal of Molecular Structure, 2012
Journal of Crystallographic and Spectroscopic Research, 1992
Journal of Molecular Modeling, 2009
The FTIR spectrum of 2-nitroaniline was recorded in the regions 4000-400 cm(-1). The optimized mo... more The FTIR spectrum of 2-nitroaniline was recorded in the regions 4000-400 cm(-1). The optimized molecular geometry, bond orders, atomic charges, harmonic vibrational wave numbers and intensities of vibrational bands of 2-nitroaniline and its cation were calculated at DFT levels invoking two different basis sets 6-31G and 6-31+G using Gaussian 03W program. The X-ray geometry and FTIR vibrational frequencies were compared with the results of DFT calculations. The thermal stability of 2NA is studied by the thermo gravimetric analysis (TGA). Experimental degradation process of 2-nitroaniline was interpreted with the bond order analysis. The Mulliken atomic charge analysis was also made in the present study. Based on the molecular geometry and Mulliken charge analysis, intra molecular hydrogen bonding was identified.
Computational and Theoretical Chemistry, 2011
ABSTRACT Quantum chemical calculations of the equilibrium geometry, harmonic vibrational frequenc... more ABSTRACT Quantum chemical calculations of the equilibrium geometry, harmonic vibrational frequencies, infrared intensities and Raman scattering activities of 2,4,6-trinitrophenol (TNP, C6H3N3O7) in the ground state were carried out by using ab initio HF and density functional theory (DFT/B3LYP) methods with 6-311++G** basis set. The research shows that the presence of strong hydrogen bonding in the title compound. The difference between the observed and scaled wavenumber values of most of the fundamentals is very small. A detailed interpretation of the infrared spectrum of TNP is also reported. The theoretical spectrograms for FT-IR of the title compound have been constructed. In addition, the HOMO and LUMO energies are also calculated.
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 2013
INDIAN JOURNAL OF …, 2008
Indian Journal of …, 2005
Abstract: A qualitative analysis of the enolic form of 3-oxo-L-gulofuranolactone (ascorbic acid) ... more Abstract: A qualitative analysis of the enolic form of 3-oxo-L-gulofuranolactone (ascorbic acid) has been made by a satisfactory vibrational band assignment using FTIR and FT Raman spectra. The calculated theoretical vibrational frequencies are compared with the ...
Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy, Jan 24, 2014
A new semi organic non linear optical polymeric crystal, bis (thiourea) silver (I) nitrate (TuAgN... more A new semi organic non linear optical polymeric crystal, bis (thiourea) silver (I) nitrate (TuAgN) with dimension 8×7×1.5 mm(3) has been successfully grown from aqueous solution by slow evaporation solution technique. Single crystal X-ray diffraction study reveals that the crystal belongs to orthorhombic system with non centrosymmetric space group C2221. The crystalline perfection of the crystal was analyzed by high resolution X-ray diffraction (HRXRD) rocking curve measurements. Functional groups present in the crystal were analyzed qualitatively by infrared and Confocal Raman spectral analysis. Effects due to coordination of thiourea with metal ions were also discussed. Optical absorption study on TuAgN crystal shows the minimum absorption in the entire UV-Vis region and the lower cut off wavelength of TuAgN is found to be 318 nm. Thermal analysis shows that the material is thermally stable up to 180°C. The mechanical strength and its parameters of the grown crystal were estimated...
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 2014
Melaminium bis(trifluoroacetate) trihydrate (MTFA), an organic material has been synthesized and ... more Melaminium bis(trifluoroacetate) trihydrate (MTFA), an organic material has been synthesized and single crystals of MTFA have been grown by the slow solvent evaporation method at room temperature. X-ray powder diffraction analysis confirms that MTFA crystal belongs to the monoclinic system with space group P2/c. The molecular geometry, vibrational frequencies and intensity of the vibrational bands have been interpreted with the aid of structure optimization based on density functional theory (DFT) B3LYP method with 6-311G(d,p) and 6-311++G(d,p) basis sets. The X-ray diffraction data have been compared with the data of optimized molecular structure. The theoretical results show that the crystal structure can be reproduced by optimized geometry and the vibrational frequencies show good agreement with the experimental values. The nuclear magnetic resonance (NMR) chemical shift of the molecule has been calculated by the gauge independent atomic orbital (GIAO) method and compared with experimental results. HOMO-LUMO, and other related molecular and electronic properties are calculated. The Mulliken and NBO charges have also been calculated and interpreted.
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 2009
Sanidine, a variety of feldspar minerals has been investigated through optical absorption, vibrat... more Sanidine, a variety of feldspar minerals has been investigated through optical absorption, vibrational (IR and Raman), EPR and NMR spectroscopic techniques. The principal reflections occurring at the d-spacings, 3.2892, 3.2431, 2.9022 and 2.6041 A confirm the presence of sanidine structure in the mineral. Sanidine shows five prominent characteristic infrared absorption bands in the region 1200-950, 770-720, 590-540 and 650-640 cm(-1). The Raman spectrum shows the strongest band at 512 cm(-1) characteristic of the feldspar structure, which contains four membered rings of tetrahedra. The UV-vis-NIR absorption spectrum had strong absorption features at 6757, 5780 and 5181 cm(-1) due to the combination of fundamental OH- stretching. The bands at 11236 and 8196 cm(-1)and the strong, well-defined band at (30303 cm(-1) attest the presence of Fe(2+) and Fe(3+), respectively, in the sample. The signals at g = 4.3 and 3.7 are interpreted in terms of Fe(3+) at two distinct tetrahedral positions Tl and T2 of the monoclinic crystal structure The (29)Si NMR spectrum shows two peaks at -97 and -101 ppm corresponding to T2 and T1, respectively, and one peak in (27)Al NMR for Al(IV).
Journal of Thermal Analysis and Calorimetry, 2009
Thermal decomposition behaviour of ten Indian limestones of marine origin have been studied by th... more Thermal decomposition behaviour of ten Indian limestones of marine origin have been studied by thermogravimetric (TG) and differential thermal analysis (DTA). DTA curves of limestone samples show asymmetric peak with index of shape about 0. 25. The size of calcite characteristic endothermic DTA peak remains unaffected due to the presence of impurities such as SiO2 and Al2O3. The presence sodium
Journal of Crystal Growth, 2013
ABSTRACT Single crystal of 2, 3-Dimethoxy-10-oxostrychnidinium hydrogen oxalate dihydrate has bee... more ABSTRACT Single crystal of 2, 3-Dimethoxy-10-oxostrychnidinium hydrogen oxalate dihydrate has been grown by slow evaporation solution growth technique (SEST) using ethanol-water solution at room temperature. It crystallizes in the orthorhombic system with space group of P212121. The crystalline perfection of the grown single crystal has been examined by high resolution X-ray diffraction analysis (HRXRD). The optical absorption studies show that the crystal is transparent in the visible region with a lower cut-off wavelength of 342 nm and the optical energy band gap Eg is found to be 3.52 eV. The electrical properties have been assessed by dielectric measurement at different temperatures. Hardness values measured using Vickers hardness indenter show considerable anisotropy. Laser damage threshold study is also carried out for the grown crystal.
Crystal Research and Technology, 2006
Applied Clay Science, 2008
Chrysotile, a variety of serpentine minerals has been investigated through optical absorption and... more Chrysotile, a variety of serpentine minerals has been investigated through optical absorption and EPR studies. High magnification electron micrographs have shown the existence of a tube-like structure of the layers. The optical absorption indicated the presence of Fe2+ and Fe3+ ions. The bands at 10,989, 11,111, 15,873 19,608, 22,727 and 26,316 cm−1 we assigned to Fe3+ and the other bands at
International Journal of Quantum Chemistry, 2000
Molecular Simulation, 2010
Thiourea is potentially capable of forming coordinate bonds through both sulphur and nitrogen eve... more Thiourea is potentially capable of forming coordinate bonds through both sulphur and nitrogen even though the extremely low basicity of the ligands militates against the formation of nitrogen-metal bonds. Both these possibilities will be reflected in the infrared spectra of the complexes. The centrosymmetric thiourea molecule when combined with inorganic salts yields non-centrosymmetric complexes, which has non linear optical properties. In the present study optically transparent crystals of Pure and doped BTMC crystals have been grown. The crystals are characterized by subjecting to Powder XRD, AAS, FTIR, UV and SHG tests are discussed and values tabulated.
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 2012
Chemical Physics Letters, 2003
International Journal of Quantum Chemistry, 2005
ABSTRACT Density functional calculations at the B3LYP/6-31G* level were performed for perylene te... more ABSTRACT Density functional calculations at the B3LYP/6-31G* level were performed for perylene tetracarboxylic dianhydride (PTCDA) and its potential derivatives modified by replacing the two anhydride ether groups with B-, N-, S-, and Se-containing groups, as well as for perylene monomer and dimer structures. The predicted infrared (IR) and Raman spectroscopic properties of PTCDA have been compared with the observed experimental spectra and available theoretical data. In addition, the isotope effect on the Raman and IR spectra of PTCDA by the replacement of all H atoms by deuterium isotopes, as well as the estimated UV-vis properties of PTCDA and its modified derivatives, based on the results of the time-dependent DFT method have been also presented. It was shown that the formation of polyperinaphthalene films affects strongly the predicted theoretically IR, Raman and UV-vis spectra of the precursor PTCDA. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005
Journal of Molecular Structure, 2012
Journal of Crystallographic and Spectroscopic Research, 1992
Journal of Molecular Modeling, 2009
The FTIR spectrum of 2-nitroaniline was recorded in the regions 4000-400 cm(-1). The optimized mo... more The FTIR spectrum of 2-nitroaniline was recorded in the regions 4000-400 cm(-1). The optimized molecular geometry, bond orders, atomic charges, harmonic vibrational wave numbers and intensities of vibrational bands of 2-nitroaniline and its cation were calculated at DFT levels invoking two different basis sets 6-31G and 6-31+G using Gaussian 03W program. The X-ray geometry and FTIR vibrational frequencies were compared with the results of DFT calculations. The thermal stability of 2NA is studied by the thermo gravimetric analysis (TGA). Experimental degradation process of 2-nitroaniline was interpreted with the bond order analysis. The Mulliken atomic charge analysis was also made in the present study. Based on the molecular geometry and Mulliken charge analysis, intra molecular hydrogen bonding was identified.
Computational and Theoretical Chemistry, 2011
ABSTRACT Quantum chemical calculations of the equilibrium geometry, harmonic vibrational frequenc... more ABSTRACT Quantum chemical calculations of the equilibrium geometry, harmonic vibrational frequencies, infrared intensities and Raman scattering activities of 2,4,6-trinitrophenol (TNP, C6H3N3O7) in the ground state were carried out by using ab initio HF and density functional theory (DFT/B3LYP) methods with 6-311++G** basis set. The research shows that the presence of strong hydrogen bonding in the title compound. The difference between the observed and scaled wavenumber values of most of the fundamentals is very small. A detailed interpretation of the infrared spectrum of TNP is also reported. The theoretical spectrograms for FT-IR of the title compound have been constructed. In addition, the HOMO and LUMO energies are also calculated.
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 2013
INDIAN JOURNAL OF …, 2008