Jet-cooled fluorescence spectra and carbonyl wagging potential energy functions of tetrahydrofuran-3-one and tetrahydrothiophen-3-one in their S-1(n,pi(*)) excited states
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abstract
The jet-cooled fluorescence excitation spectra of states of tetrahydrofuran-3-one and tetrahydrothiophen-3-one have been recorded and analyzed. The carbonyl inversion bands, which arise from double-minimum potential energy functions in the excited states, were fit with functions of the form V = ax4 -bx2 or V = cx2 + d exp(-fx2). The furanone was found to have an inversion barrier in the S1(n,*) state of 1152 cm-1 (13.8 kJ mol-1) while the thiophenone has a barrier of 659 cm-1 (7.9 kJ mol-1). The two molecules have their potential energy minima for the S1(n,*) state at carbonyl wagging angles of 26 and 20, respectively. The results here, together with previous data for several other cyclic ketones, demonstrate that the inversion barrier increases with the ring angle strain at the ketone carbon atom.
