Spectroscopic and Theoretical Determination of the Structure of 2,6-Difluoropyridine in Its Ground and Excited Electronic States

ORAL

Abstract

The infrared and Raman spectra of 2,6-difluoropyridine (26DFPy) along with \textit{ab initio} and DFT computations have been used to assign the vibrations of the molecule in its S$_{0}$ electronic ground state and to calculate its structure. The ultraviolet absorption spectrum showed the electronic transition to the S$_{1}(\pi $,$\pi $*) state to be at 37,820.2 cm$^{-1}$. With the aid of \textit{ab initio} computations the vibrational frequencies for this excited state were also determined. TD-B3LYP and CASSCF computations for the excited states were carried out to calculate the structures for the S$_{1}(\pi $,$\pi $*) and S$_{2}$(n,$\pi $*) excited states. The CASSCF results predict that the S$_{1}(\pi $,$\pi $*) state is planar and the S$_{2}$(n,$\pi $*) state has a barrier to planarity of 256 cm$^{-1}$. The TD-B3LYP computations predict a barrier of 124 cm$^{-1}$ for the S$_{1}(\pi $,$\pi $*) states, 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 $\pi $ bonding within the pyridine ring.

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Authors

  • Jaan Laane

    Texas A\&M Univ

  • Hanu Arava

    University of Houston, University of Texas at Brownsville, None, Univ of Texas, San Antonio, University of Texas at El Paso, Univ of Arizona, Department of Physics and Astronomy and Center for Gravitational Wave Astronomy, University of Texas at Brownsville, Laboratoire des Mat\'eriaux Avanc\'es, Universit\'e Claude Bernard Lyon 1, UTEP, University of Texas, Austin, University of Texas at Austin, Institute for Astronomy, Russian Academy of Sciences, University of Texas at Arlington, The University of Texas at Arlington, MIT, U. Mass. Dartmouth, Texas A{\&}M University, Texas Christian University, Laboratoire des Mat\'erieux Avanc\'es B\^atiment Virgo, Ion Beam Materials Laboratory, Los Alamos National Laboratory, Texas A\&M University, Accelerator Research Laboratory, University of Florida, The Ohio State University, Yale University, University of Guelph, Canada, Armagh Observatory, NASA-Ames, NASA-Goddard, Texas A\&M University-Commerce, Texas A\&M University, Hanyang University, Texas A\&M Univ, Department of Pharmacy, Mazandaran University of Medical Sciences, Sari, Iran, Physics Department, Texas State University at San Marcos

  • Hanu Arava

    University of Houston, University of Texas at Brownsville, None, Univ of Texas, San Antonio, University of Texas at El Paso, Univ of Arizona, Department of Physics and Astronomy and Center for Gravitational Wave Astronomy, University of Texas at Brownsville, Laboratoire des Mat\'eriaux Avanc\'es, Universit\'e Claude Bernard Lyon 1, UTEP, University of Texas, Austin, University of Texas at Austin, Institute for Astronomy, Russian Academy of Sciences, University of Texas at Arlington, The University of Texas at Arlington, MIT, U. Mass. Dartmouth, Texas A{\&}M University, Texas Christian University, Laboratoire des Mat\'erieux Avanc\'es B\^atiment Virgo, Ion Beam Materials Laboratory, Los Alamos National Laboratory, Texas A\&M University, Accelerator Research Laboratory, University of Florida, The Ohio State University, Yale University, University of Guelph, Canada, Armagh Observatory, NASA-Ames, NASA-Goddard, Texas A\&M University-Commerce, Texas A\&M University, Hanyang University, Texas A\&M Univ, Department of Pharmacy, Mazandaran University of Medical Sciences, Sari, Iran, Physics Department, Texas State University at San Marcos