Unimolecular decomposition of chemically activated deutero-substituted ethanol molecules studied by infrared chemiluminescence from H2O, HOD, and D2O

Vibrationally excited H2O, HOD, and D2O molecules formed by unimolecular elimination from deutero-substituted ethanol molecules C2H5OH*, C2H5OD*, CH2DCH2OH*, and CH2DCH2OD* with an excitation energy of about 100 kcal mol(-1) were observed by infrared chemiluminescence in the 2400-3900 cm(-1) range. The activated ethanol molecules were produced via the successive reactions H+CH2ICH2OH-->HI+CH2CH2OH and H+CH2CH2OH-->CH3CH2OH* in a fast flow reactor that was observed with a Fourier transform spectrometer. The vibrational distributions of the H2O, HOD, and D2O molecules were determined by computer simulation of the experimental spectra; the distributions decline with increasing vibrational energy giving [f(v)]=0.15 and [f(v)]=0.14 for H2O and HOD from the decomposition of C2H5OH* and C2H5OD*, respectively. The vibrational energy in the bending mode of H2O is comparable to the energy in the stretching modes. Comparison with the statistical vibrational distributions shows a substantial overpopulation of the bending levels and a preferential excitation of one O-H or O-D stretching quantum in HOD from C2H5OD or CH2DCH2OH, respectively, i.e., in the newly formed bond. Kinetic isotope effects of [H2O]/[HOD]=3.6+/-0.8 and [HOD]/[D2O]=3.1+/-0.8 were found for the two elimination pathways of CH2DCH2OH* and CH2DCH2OD*, respectively, which agree with calculated RRKM values of k(H2O)/k(HOD) = 3.2 and k(HOD)/k(D2O) = 2.7. (C) 1996 American Institute of Physics.