Vibrational energy distribution of CD2(1A1) from ketene-d2 photolysis upon reaction with cyclobutane. A chemically activated methylcyclobutane study

The results of a study of chemically activated methylcyclobutane and methylcyclobutane-d2 from the 337-, 334-, and 313-nm photolyses of ketene or ketene-d2 in the presence of cyclobutane, tetramethylsilane, and oxygen are presented. The collisional deactivation of the chemically activated molecules was found to occur in steps of 6 +/- 2 kcal/mol. A critical examination of the uncertainties in collisional deactivation stepsize determinations in chemical activation systems is given. The vibrational energy distribution of the CH2(1A1) and CD2(1A1) at the time of reaction with cyclobutane are determined and discussed. The distributions were found to broaden giving increasing average methylene energies with increasing photon energies and with deuterium substitution on the CH2. An interesting quantum statistical isotope effect on the width of these distributions in going from the 337- to 313-nm photolysis systems is observed and explained in terms of the CH2(1A1) and CD2(1A1) vibrational frequency models. This is an energy partitioning isotope effect on CH2CO vs. CD2CO photodissociations. A statistical energy partitioning model for CH2CO and CD2CO photodissociation was found to give generally narrower methylene vibrational energy distributions and lower average energies than observed. 19 references, 10 figures, 6 tables