A new determination of the dissociation energy of acetylene

Publisher Website
Google Scholar
Abstract
A new upper bound for the dissociation energy of acetylene, D00(HCC–H) =529.89(±0.01) kJ/mol, has been determined by Stark anticrossing spectroscopy. The zero-pressure extrapolated (unimolecular) decay rates of levels of S1 (Ã 1Au) v′3=2 and 3 (quanta of the trans-bending vibration) increase upon application of an electric field of 113 kV/cm. We attribute this increase in molecular decay rate to predissociation rather than any other Stark-induced nonradiative or radiative phenomenon. The lowest level (v′3 =2, J′=2, K′=1) from which we have observed an increase in decay rate (i.e., predissociation) has an internal energy of 44 295.65 cm−1 relative to v=0, J=0 of S0 (X̃ 1∑+g). This corresponds to a value about 24 kJ/mol lower then the consensus upper bound result from four different recent experimental determinations (including one of ours) as well as current ab initio results. The new value agrees, however, with earlier work and with recent modeling studies of acetylene pyrolysis kinetics.