Knowledge Bank

Recently we reported [J. Chem. Phys. 91, 5160(1989)] an upper bound measurement of $D00(HCC-H)\le 126.65kcal/mol$, based on observations of Stark-induced increases in radiative decay rates of securely assigned rovibronic levels of the $HCCHA~1Au$ state. The lowest level to show a significant zero-pressure-extrapolated lifetime decrease (from 667(5)ns at $\epsilon =0volts/cmto514(4)ns$ at $\epsilon =113kV/cm$) is $v3=2,Ka=1,J=1$ at $44295.65(10)cm-1$ above $v\prime \prime =0,J\prime \prime =0$ of the $X¯$-state. Our interpretation of this Stark-induced lifetime decrease as predissociation has been the subject of considerable controversy, owing to the importance of $D00(HCC-H)$ and $\Delta H10(HCC)$ in models of combustion kinetics and to recent reports of experimental and ab initio values 5-7 kcal/mol larger than our upper bound value. Alternative interpretations of our Stark effect result and other conflicting experimental results will be discussed.