DIRECT OBSERVATION OF THE UNIMOLECULAR DECOMPOSITION OF TETRAMETHYLDIOXETANE INDUCED BY SINGLE PHOTON OVERTONE EXCITATION

Tetramethyldioxetane (TMD) was excited by overtone absorption to v = 3, v = 4, and v = 5 of the C-H stretch vibration. By observing the chemiluminescence that accompanied the resulting decomposition, the rates of the unimolecular reaction and collisional quenching of TMD excited to v = 4 and v = 5 were directly measured in a time resolved manner down to pressures low enough that the collisional contribution to the lifetime of the excited TMD was only a few percent. The intensity of the emission as a function of excitation wavelength was found to be in good agreement with the local mode model for these overtones. In addition, from the time dependence of the chemiluminescence it was found that there is an emitting product, which is different from either triplet acetone or singlet acetone. This radiating product is also formed upon excitation of TMD in the long wavelength tail of its electronic absorption.