Ab initio study of the structured and conformations of 2-fluoroethanal in the ground and lowest excited electronic states

The structure of the conformationally flexible 2-fluoroethanal molecule (CH 2FCHO, FE) in the ground (S-0) and lowest excited triplet (T-1) and singlet (S-1) electronic states was investigated by ab initio quantum-chemical met hods. The FE molecule in the So state was found to exist as two conformers, viz., as cis (the F-C-C-O angle is 0 degrees) and trans (the F-C-C-O angle is 180 degrees) conformers. On going both to the T-1 and S-1 states, the F E molecule undergoes substantial structural changes, in particular, the CH2 F top is rotated with respect to the core and the carbonyl CCHO fragment be comes nonplanar. The potential energy surfaces for the T-1 and S-1 states a re qualitatively similar, viz., six minima in each of the excited states of FE correspond to three pairs of mirror-symmetrical conformers. Based on th e potential energy surfaces calculated for the FE molecule in the T-1 and S -1 states, the one-dimensional problems on the torsion and inversion nuclea r motions as well as the two-dimensional torsion-inversion problems were so lved.