Electronic spectroscopy of ethanol: An experimental and theoretical study

Abstract

The electronic spectrum of ethanol (CH3CH2OH) in the 6–11 eV region is analysed by recording its photoabsorption spectrum using synchrotron radiation source. The electronic spectra comprise predominately weak Rydberg series of ns and np type converging to the first three ionization potentials overriding a broad continuum. DFT calculations on the neutral and ionic ground states of ethanol conformers predicted an unusual large CC bond length for gauch conformers (1.759 Å) at its ionic limit resulting in unimolecular dissociation at 0.28 eV below the ionization potential of trans conformer. Vertical excited state energies computed at TDDFT/CAMPB3LYP level of theory gave an excellent correlation of the experimentally observed spectral features. In the present work the assignment of the observed Rydberg peaks in the VUV region could be adequately interpreted by taking into consideration the presence of excitations from both trans and gauche conformers of ethanol. The no-3p Rydberg transition and associated vibronic features showed the presence of both conformers in the 7.5–8.5 eV region of electronic spectrum. Plots of the potential energy curve plots of the first few excited states gave insight into the nature of the excited states and confirmed that the lowest state to be dissociative in nature. This is a first report of the comprehensive electronic spectroscopic study of conformers of ethanol in the VUV region.