EXPERIMENTAL AND AB-INITIO THEORETICAL-STUDY OF THE KINETICS OF REARRANGEMENT OF KETENE IMINE TO ACETONITRILE

When heated by reflected shock waves to temperatures between 1400 and 1700 K at pressures of approximately 12-15 arm, mixtures of acetonitri le in argon (0.4-7 mol %) exhibit strong banded absorption in the ultr aviolet region between 320 and 250 nm. The carrier of the absorption s pectrum is ketene imine, H2C=C=NH. Time-resolved spectra of ketene imi ne have been recorded with exposure times between 100 and 200 mu s usi ng a charge-coupled device (CCD) with an imaging spectrograph. Through the use of the technique of pixel binning, temporal profiles of forma tion and equilibration of ketene imine have been obtained with a time resolution of 24 mu s. The rearrangement of ketene imine <-> acetonitr ile has been studied using ab initio quantum chemical techniques. The calculations predict the rate-determining step in the rearrangement pr ocess to be the 1,2-hydrogen transfer of the imine hydrogen to the adj acent carbon atom to produce vinyl nitrene. With the aid of the ab ini tio results, the experimental rate data for the reaction ketene imine --> acetonitrile have been extrapolated to the high-pressure limit, yi elding the rate constant expression k(infinity) = 10(13.4(+/-0.5)) exp (-294(+/-14) kJ mol(-1)/RT) s(-1).