FAR-INFRARED SPECTRA AND 2-DIMENSIONAL POTENTIAL-ENERGY SURFACES FOR THE OUT-OF-PLANE RING VIBRATIONS OF TETRAHYDROFURAN-3-ONE IN ITS S-0 AND S-1(N,PI-ASTERISK) ELECTRONIC STATES

The far-infrared spectra of tetrahydrofuran-3-one show ring-bending (1 00-120 cm(-1)), ring-twisting (227-237 cm(-1)), difference (115-137 cm (-1)), and overtone (200-225 cm(-1)) bands. Calculations for the two-d imensional potential energy surface governing the twisting and bending motions were carried out. The minima of the potential surface corresp ond to twisted conformations with twist angles of approximately +/-35 degrees. The barrier to planarity is in the 1500 to 2000 cm(-1) range. No saddle points corresponding to bent structures are present for the surface. A potential energy surface for the S-1(n,pi) excited state, based on previous fluorescence excitation data, was also calculated. The latter has an assumed barrier to planarity of 1400 cm(-1) and a ba rrier to pseudorotation of 880 cm(-1). (C) 1998 American Institute of Physics. [S0021-9606(98)00621-7]