IR spectra of nitrobenzene and nitrobenzene-15 N in the gas phase, ab initio analysis of vibrational spectra and reliable force fields of nitrobenzene and 1,3,5-trinitrobenzene. Investigation of equilibrium geometry and internal rotationстатья
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Дата последнего поиска статьи во внешних источниках: 23 ноября 2015 г.
Аннотация:Abstract The IR spectra of gaseous nitrobenzene (NB)
and its 15N isotopomer have been obtained in the frequency
range of 3500–250 cm-1, and the far-IR spectra of their
solutions and the NB neat liquid sample have been recorded
in the range of 600–30 cm-1. A detailed description of
the spectra of NB and 1,3,5-trinitrobenzene (sym-TNB) and
their isotopomers has been accomplished using the force
fields calculated at the MP2(full)/aug-cc-pVTZ and
MP2(full)/cc-pVTZ levels. Transferability of the refined
scale factors for the calculated force constants obtained by
the Pulay technique has been used to provide evidence for
validity of both interpreting the NB and sym-TNB spectra
and refining the calculated force fields. The direct and
inverse spectral problems have been solved by variational
technique to determine torsional energy levels and refine
the potential function by optimizing the Vk coefficients in
its Fourier series expansion. The height of the MP2(full)
barrier to internal rotation has been reduced from 5.5 to
4.5 kcal/mol due to extension of the used basis set from
6-31(d,p) to aug-cc-pVTZ. The method of joint dynamic
structural analysis of the GED, MW, and vibrational
spectroscopy, and ab initio data in terms of the PES
parameters have been applied to investigation of equilibrium
geometry and internal rotation in the nonrigid NB and
sym-TNB molecules having one and three coupled internal
rotors, respectively. The experimental re-parameter values
of both molecules (C2v and D3h point group symmetries)
are in agreement with those obtained by ab initio calculations.