Infrared,
Raman, and Ultraviolet Absorption Spectra and Theoretical Calculations
and Structure of 2,6-Difluoropyridine in Its Ground and Excited Electronic
States
posted on 2013-12-19, 00:00authored byHong-Li Sheu, Sunghwan Kim, Jaan Laane
The
infrared and Raman spectra of 2,6-difluoropyridine (26DFPy) along
with ab initio and DFT computations have been used to assign the vibrations
of the molecule in its S0 electronic ground state and to
calculate its structure. The ultraviolet absorption spectrum showed
the electronic transition to the S1(π,π*) state
to be at 37 820.2 cm–1. With the aid of ab
initio computations the vibrational frequencies for this excited state
were also determined. TD-B3LYP and CASSCF computations for the excited
states were carried out to calculate the structures for the S1(π,π*) and S2(n,π*)
excited states. The CASSCF results predict that the S1(π,π*)
state is planar and that the S2(n,π*)
state has a barrier to planarity of 256 cm–1. The
TD-B3LYP computations predict a barrier of 124 cm–1 for the S1(π,π*) state, but the experimental
results support the planar structure. Hypothetical models for the
ring-puckering potential energy function were calculated for both
electronic excited states to show the predicted quantum states. The
changes in the vibrational frequencies in the two excited states reflect
the weaker π bonding within the pyridine ring.