he photodissociation of oxetane at 193 nm as the reverse of theaterno-Buchi reaction

摘要

We investigated the photodissociation of oxetane (1,3-trimethylene oxide) at 193.3 nm in amolecular-beam apparatus using photofragment-translational spectroscopy and selectivephotoionization. We measured time-of-flight (TOF) spectra and angular anisotropy parameters /3(t)as a function of flight time of products at m/ z =26-30 u utilizing photoionization energies from 9.8to 14.8 eV. The TOF distributions of the products alter greatly with the employed photon energy,whereas their β(t) distributions are insensitive to the photon energy. Dissociation to H_2CO+C_2H_4isthe major channel in the title reaction. Three distinct dissociation paths with branching ratios0.923:0.058:0.019 are responsible for the three features observed in the distribution of kineticenergy released in the channel H_2CO+C_2H_4. The observation ofH_2and H atoms, ~1% inbranching, indicates that products H_2COand C_2H_4spontaneously decompose to only a small extent.Most HCO, C_2H_3, and C_2ions originate from dissociative photoionization of products H_2CO andC_2H_4. Except atomic H andH_2,the photoproducts have large angular anisotropies, β≥-0.8, whichreflects rapid dissociation of oxetane following optical excitation at 193.3 nm. The mechanisms ofdissociation of oxetane are addressed. Our results confirm the quantum-chemical calculations ofPalmer et al. and provide profound insight into the Paterno-Buchi reaction.