LIF excitation spectra of jet-cooled 3,5-dicyanoaniline

Abstract

The infrared and Raman spectra for crystalline 3,5-dicyanoaniline (3,5-DCA) and the laser induced fluorescence (LIF) excitation spectra of vacuum jet cooled molecules have been investigated. The ground S₀(A₁) and excited S₁(B₂) state geometries, charge distributions and vibrational frequencies of 3,5-DCA have been evaluated by ab initio calculations. The Dushinsky matrices have been used for the mode correlation and assignments of the transition frequencies in LIF excitation spectra of 3,5-DCA (−NH₂) and 3,5-DCA(−ND₂) as well as the IR and Raman spectra for deuterated species. It has been found that the transitions I²₀ involving inversion motion of the amino group in 3,5-DCA show remarkable intensities suggesting substantial change in the potential energy function upon electronic excitation for the out-of-plane motion of the hydrogen atoms in the amino group. The barrier height for the inversion in the ground electronic state of 3,5-DCA seems to be the same order as the zero point energy. For the lowest excited electronic state the potential function for the inversion has single minimum but shows substantial anharmonicity. The intensity distribution in the LIF excitation spectrum has been modeled using multidimensional Franck–Condon factors. Geometry changes for S₀ → S₁ excitation of 3,5-DCA are discussed.