DECOMPOSITION OF CHEMICALLY ACTIVATED ETHANOL

The infrared chemiluminescence from vibrationally excited H2O molecules in the 3200-4000 cm(-1) range was observed from the unimolecular decomposition of C2H5OH* in a fast flow reactor coupled with a Fourier transform infrared spectrometer. Activated ethanol molecules were generated via the successive reactions H + CH2ICH2OH --> HI + CH2CH2OH and H + CH2CH2OH --> CH3CH2OH*; the excitation energy of C2H5-OH is about 100 kcal mol(-1). Simulation of the experimental spectrum was made using the available absorption intensities for upsilon(1), 2 upsilon(2), and upsilon(3) bands of H2O. The main contributions are from the (O upsilon(2)1) - (O upsilon(2)0) and (O upsilon(2)2) --> (O upsilon(2)1) transitions with extensively excited bending vibrations. The energy distribution for H(2)0 agrees with the general picture for the dynamics of four-centered-elimination reactions of halo-substituted alkanes for which only a small fraction of the potential energy is released as vibrational energy to the eliminated product. Ab initio and RRKM calculations have been carried out in order to compare the statistical reaction probabilities for the H2O + C2H4, C2H5 + OH, and CH3 + CH2OH unimolecular decomposition pathways of ethanol. The ab initio results suggest that the threshold energy for H2O elimination from ethanol is less than or equal to 67 kcal mol(-1).