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1. Photoabsoption spectroscopy studies on Difluoromethane (CH2F2)
Difluoromethane is an important new generation refrigerant belonging to the family of hydrofluorocarbons (HFC’s). These compounds are replacements for the ozone depleting chlorofluorocarbons (CFC’s) in the refrigeration industry. HFC’s are considered to have zero ozone depletion potential. However, since considerable quantities of HFC’s would be released into the atmosphere in the future, it is of interest to study the effect of extreme UV radiation on these molecules. The vacuum ultraviolet (VUV) absorption spectrum of difluoromethane (CH2F2) was studied using monochromatic synchrotron light from Photophysics beamline at Indus-1. Spectra were recorded in the spectral region 1050 – 1500 Å (~8.3 – 11.8 eV) at a resolution of 1.5 Å. Three absorption band systems were observed in this region. Discrepancies in assignments of the observed vibronic bands carried out by previous workers have been resolved. The observed bands have been classified in terms of Rydberg series. The results are going to appear in “Spectroscopy letters” journal as a paper.
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2. Diffuse reflectance measurements on multilayers:
Diffuse reflectance or optical scattering in thin films and multilayers can pose serious limiting factors to their desired or ultimate performances. Besides, such studies provide valuable information related to the buried microstructures and interfaces. Synchrotron radiation is the most appropriate source to record wavelength dependent polarized light scattering in thin films and multilayers. In the present experiment several gadolinia, silica thin films and multilayers were studied for their light scattering using the white light synchrotron beam. Various thin film layer geometries were selected to probe the results due to different types and combinations of interfaces. Due to phase coherent delay in certain optical non-wedged component used in the experimental setup very interesting spectral interference were noticed as the modulations in the diffuse reflectance signal. Appropriate modeling approach utilizing Gaussian function de-convolution technique is used to compute the pulse delay between the back reflected and forward propagating scattering signals that lead to such spectral interference. Alternatively inverse fast Fourier transform (IFFT) and analytical techniques were adopted to determine the group delays. The diffuse reflectance spectra were finally compared with their specular counter part and a shift both in the wavelength and phase were noticed. This may be explained on the basis of thin film roughness factors, different polarizations and incident geometries used in the measurements. However, all most all the spectral scattering signals exhibited the features resembling their specular reflection characteristic.
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Latest publications:
- Aparna Shastri, B.N.Raja Sekhar, Param Jeet Singh and M.N. Deo, “The Vacuum Ultraviolet (VUV) Absorption Spectrum of Difluoromethane (CH2F2) Reinvestigated” Spectroscopy letters – in press.
- N.K. Sahoo, S.Thakur, B.R.Tokas and B.N. Raja Sekhar, “ Spectral diffuse reflectance measurements of gadolinia, silica thin film systems using synchrotron radiation , Applied surface science, Vol. 253, 4515-4523, 2007.
- N. K. Sahoo, S. Thakur, R. B. Tokas and B. N. Raja Sekhar , “Observation and analysis of spectral interference modulations in thin film light scattering experiments using synchrotron radiation”, J. Phys. D: Appl. Phys. 39 4059 - 4067(2006).
- P. Sharma, R.K. Vatsa, B.N. Rajasekhar, N.C. Das, T.K. Ghanty and S.K. Kulshreshtha, “C State mediated photoionization of CH3I in visible and near UV region”. Rapid communications in mass spectrometry,Vol19, 1522(2005).
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