DECOMPOSITION OF CHEMICALLY ACTIVATED ETHANOL

The infrared chemiluminescence from vibrationally excited H2O molecule s in the 3200-4000 cm(-1) range was observed from the unimolecular dec omposition of C2H5OH in a fast flow reactor coupled with a Fourier tr ansform infrared spectrometer. Activated ethanol molecules were genera ted via the successive reactions H + CH2ICH2OH --> HI + CH2CH2OH and H + CH2CH2OH --> CH3CH2OH; the excitation energy of C2H5-OH is about 1 00 kcal mol(-1). Simulation of the experimental spectrum was made usin g the available absorption intensities for upsilon(1), 2 upsilon(2), a nd upsilon(3) bands of H2O. The main contributions are from the (O ups ilon(2)1) - (O upsilon(2)0) and (O upsilon(2)2) --> (O upsilon(2)1) tr ansitions with extensively excited bending vibrations. The energy dist ribution for H(2)0 agrees with the general picture for the dynamics of four-centered-elimination reactions of halo-substituted alkanes for w hich only a small fraction of the potential energy is released as vibr ational energy to the eliminated product. Ab initio and RRKM calculati ons have been carried out in order to compare the statistical reaction probabilities for the H2O + C2H4, C2H5 + OH, and CH3 + CH2OH unimolec ular decomposition pathways of ethanol. The ab initio results suggest that the threshold energy for H2O elimination from ethanol is less tha n or equal to 67 kcal mol(-1).