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Chapter III CHN Analysis, FT IR …..
crystal is suggested to be the cause for the broadening of the peak. The peaks
below 1200 cm −1 are due to PO4 vibrations. The broad envelopes observed
between 2300 and 3600 cm −1 are mainly due to P–OH stretching of H2PO4.
Govani et al [20] have studied the interaction of L-arginine with KDP crystal by
FTIR and Raman spectroscopy. They have confirmed the interaction by
additional vibrational line originating from the distributed N-H, C-H and C-N
bonds of L-arginine. They also suggest the possibility of Hydrogen bonding
primarily between the nucleophilic-O of phosphate unit of KDP with amino
group of arginine. It has been found that the weak interaction of the dopants
with one of the O-H groups of KDP and possible entry of dopants into the lattice
sites of the crystal leads to the decrease in the frequency and confirms the
nonlinear optical nature in pure and doped crystals [21]. The FT – IR spectra
for both pure and various amino acids doped KDP crystals are presented in
figure (3.7 to 3.10) and assignments are given in table (3.3). Some additional
absorption peaks are observed in spectra of amino acids doped KDP crystals,
which is, a clear indication of successful doping of different amino acids in KDP
crystals. Nevertheless, from the assignments of various absorption peaks in
FTIR spectra, the general natural of spectra can be deduced. The absorption
peaks at 3580 cm -1 for pure KDP crystal and the absorptions within 3445 cm -1
to 3481.7 cm -1 for amino acids doped KDP crystals are due to O-H stretching
vibration and N-H stretching vibration. However, there is a possibility of overlap
of O-H and N-H asymmetric stretching vibrations in case of amino acids doped
KDP crystals. The reduction absorption peak values may be due to either the
overlap or the hydrogen bond interaction with amino group.
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