Dynamics of multi-channel dissociation of tetrahydrofuran photoexcited at 193 nm: distributions of kinetic energy, angular anisotropies and branching ratios

Abstract

We investigated the photodissociation dynamics of tetrahydrofuran (c-C(4)H(8)O) at 193.3 nm in a molecular-beam apparatus using photofragment-translational spectroscopy and direct vacuum-ultraviolet (VUV) photoionization. Five dissociation channels leading to products with m/z ratios appropriate for CH(2)CH(2)CH(2) + H(2)CO, CH(2)CHCH(2) + CH(2)OH, H + CH(2)CH(2) + CH(2)CHO, CH(2)CH(2) + CH(3) + HCO and CH(2)CH(2) + CH(2)CO + H(2) were identified; their branching ratios were determined to be 0.40, 0.25, 0.04 0.29 and 0.02, respectively. Secondary dissociations from nascent products CH(2)CH(2)CH(2)CHO to CH(2)CH(2) + CH(2)CHO and from CH(2)CH(2)O to CH(3) + HCO and likely to CH(2)CO + H(2) were observed. We measured distributions of product kinetic energy, average kinetic-energy release, and fractions in translation for each dissociation channel. The formation of CH(2)CHCH(2) + CH(2)OH indicates that hydrogen migration occurs before complete fragmentation. All photofragments have nearly isotropic angular distributions, with |beta| values less than 0.05. The photodissociation of tetrahydrofuran into five channels is proposed to proceed mainly on the ground state potential-energy surface following ring opening and efficient internal conversions.