A. Ramoji et al. / Spectrochimica Acta Part A 68 (2007) 504–509
509
In assessing the performance of RHF and B3LYP we find that
the frequencies predicted by them near 3000 cm−1 agree well
with observed values within 1%. For all other frequencies from
3000downto700 cm−1 theerrorshoveraround6%. Intheregion
700–120 cm−1, the B3LYP frequencies near 500 cm−1 are in
excellent agreement with experiment; the deviations increase
for both the methods below 500 cm−1, reaching almost 10%.
In terms of mean absolute deviation, 18 cm−1 with root-mean-
square error of 21 cm−1 are for B3LYP frequencies as against
24 and 33 cm−1 for RHF frequencies.
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5. Conclusions
The equilibrium geometry of 3-acetylcoumarin has been
obtained at RHF and B3LYP levels of theory using the 6-
31G(d,p) basis set. While B3LYP has performed better than
RHF as far as the bond lengths are concerned, both the methods
have performed nearly to the same level across the bond angle
sets. Infrared and Raman spectra of 3-acetylcoumarin have been
assigned on the basis of group-frequency correlation supported
by the theoretical harmonic frequency analysis. The carbonyl
vibrations in the pyrone ring and the acetyl group have been very
accurately predicted by B3LYP/6-31G(d,p) level. In several of
the normal modes, the contributions of different bond oscillators
has been demonstrated. The vibrational spectrum predicted by
the theoretical level B3LYP/6-31G(d,p) is in good agreement
with the experimental spectrum.
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Acknowledgements
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We are greatly indebted to Dr. S. Umapathy, Dept. of
Inorganic and Physical Chemistry, Indian Institute Science,
Bangalore, and Professor B.G. Mulimani, Vice-Chancellor, Gul-
burga University. Raman spectral recording at SAIF, Indian
Institute of Technology, Chennai, is gratefully acknowledged.
One of us, Anuradha Ramoji, acknowledges the UGC DSA
(Phase-III) for the award of Project Fellowship.
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