Evidence of CH2O (ã 3A2) and C2H4 (ã 3B1u) produced from photodissociation of 1,3-trimethylene oxide at 193 nm.

We investigated the dissociative ionization of formaldehyde (CH₂O) and ethene (C₂H₄) produced from photolysis of 1,3-trimethylene oxide at 193 nm using a molecular-beam apparatus and vacuum-ultraviolet radiation from an undulator for direct ionization. The CH₂O (C₂H₄) product suffers from severe dissociative ionization to HCO⁺ (C₂H₃⁺ and C₂H₂⁺) even though photoionization energy is as small as 9.8 eV. Branching ratios of fragmentation of CH₂O and C₂H₄ following ionization are revealed as a function of kinetic energy of products using ionizing photons from 9.8 to 14.8 eV. Except several exceptions, branching ratios of daughter ions increase with increasing photon energy but decrease with increasing kinetic energy. The title reaction produces CH₂O and C₂H₄ mostly on electronic ground states but a few likely on triplet states; C₂H₄ (∼³ B_1u) seems to have a yield greater than CH₂O (ã³ A₂). The distinct features observed at small kinetic energies of daughter ions are attributed to dissociative ionization of photoproducts CH₂O (ã³A₂) and C₂H₄ (ã³B_1u). The observation of triplet products indicates that intersystem crossing occurs prior to fragmentation of 1,3-trimethylene oxide. [ABSTRACT FROM AUTHOR]