PHOTOFRAGMENTATION OF ACETYL CYANIDE AT 193 NM

The photodissociation of gaseous acetyl cyanide has been examined foll owing excitation at 193 nm. CN X(2) Sigma(+) photofragments were probe d via laser fluorescence excitation to determine their rotational, vib rational, and translational energy distributions. CN was produced in v '' = 0 and 1 with mean rotational energy (13.5 +/- 2) kJ mol(-1), and v'' = 2 with mean rotational energy (10 +/- 4) kJ mol(-1). Mean transl ational energies of the CN fragments were (32 +/- 10) kJ mol(-1). Ab i nitio electronic structure theory has been used to characterize the he at of formation for acetyl cyanide along with its geometries and vibra tional frequencies. The acetyl cyanide heat of formation, Delta H0(f,0 ), is predicted to be (-0.4 +/- 8) kJ mol(-1) using Gaussian-2 theory (G2). The theoretical results are used to compute bond dissociation en ergies of acetyl cyanide for further interpretation of the experimenta l photodissociation data. Evidence is presented that the majority of C N fragments are produced via dissociation of the parent acetyl cyanide to CH3CO + CN, with subsequent decomposition of the acetyl fragment. The alternate possible primary alpha-cleavage pathway to CH3 + OCCN is proposed as a possible source for the OCCN radical.