A CASSCF and CASPT2 study of the photochemistry of 1,1- and 1,2-difluoroethylenes

Conical Intersections and Low‐Lying Electronic States of Tetrafluoroethylene

“…In particular, our computations support the experimental evidence that the relaxation to the ground state proceeds via an intermediate valence π–π* state and is accompanied by twisting and pyramidalization. Our research is also consistent with earlier theoretical studies of the low‐lying excited states of the related C 2 H 4 and C 2 H 2 F 2 molecules,19, 23 for which similar relaxation pathways have been predicted. For C 2 H 4 , the relative energies of the V–N MECIs along pyramidalization and H migration pathways were computed by Lischka and co‐workers to be 4.7 and 4.9 eV, respectively,19 which demonstrates that the V–N conical intersection along the C 2 F 4 pyramidalization pathway is much more accessible energetically than that for C 2 H 4 .…”

“…The excited states of C 2 F 4 have been much less studied than those of C 2 H 4 17–22 and C 2 H 2 F 2 23. The electronic spectrum of C 2 F 4 has been investigated using UV spectroscopy24, 25 and electron‐impact spectroscopy 25.…”

Internal energy of HCl upon photolysis of 2-chloropropene at 193 nm investigated with time-resolved Fourier-transform spectroscopy and quasiclassical trajectories

“…39 Moreover, conical intersections between excited and ground electronic states might promote reaction pathways that have not been considered in this study. In fact, multiconfigurational and multireference ab initio calculations on vinyl fluoride 40 and difluoroethylenes 41 have shown S 0 / S 1 conical intersections associated with hydrogen migration, which might play a significant role in the photodissociation of these systems through increasing the probability of this process.…”

Non-adiabatic photoisomerization versus photodissociation dynamics of the chiral fluoroethylene derivative (4-methylcyclohexylidene) fluoromethane

“…Note that the coupling elements T R 12 are negligible along both coordinates, a fact that substantiates the diabatization path chosen in Eq. (12). Since the adiabatic V ad 1 and V ad 2 potentials are symmetric and cyclic along the torsion coordinate, one expects the corresponding diabatic ones V d 1 and V d 2 to be symmetric and cyclic, too.…”

“…Similarly, elimination of halogen derivatives has been detected in difluoroethylenes [15][16][17] and vinyl chloride [18,19]. The photodissociation dynamics of ethylene [20], fluoroethylene [21,22], difluoroethylenes [12,[23][24][25] and vinyl chloride [26,27] have also been investigated from the theoretical point of view.…”