Theoretical Study on Potential Energy Surface of the C₂H₂FO Radical

Abstract

The potential energy surface of C2H2FO is investigated at CCSD(T)/6-311G(d,p)//B3LYP/6-311G(d,p) level. The results show that isomers of 1, 3, 4, 5, 5‘, 8, 9, and 9‘ are stable, and the energy barriers are more than 30 kcal/mol. Isomer 2 has, relatively speaking, much lower kinetic stability. The three cyclic isomers 6, 6‘, and 7 are less stable than the former, but more stable than the latter. The other isomers, such as isomers 1‘, 3‘, 4‘, 10, and 11 are less stable than isomer 2 in kinetics. Only isomer 1 was synthesized experimentally, and the calculated frequencies are in good agreement with experimental values, so we conjecture that in the future, other stable isomers may be synthesized by the experimental methods, for example, coming from such reactions as FCCH + OH, CH2F + CO, and so forth. Compared to the analogous C2H3O radical isomers, the energy order is changed. This may be due to conjugation of the carbonyl group in isomer 1 CH2CFO with the substituent fluorine at the α-position.

Photodissociation spectroscopy and dynamics of the CH2CFO radical

“…The frequencies presented in Table IV have been scaled by a factor of 0.9538 as recommended by Scott and Radom 42 for the QCISD/6-31G(d) level of theory. Additionally, the total ab initio energies are given in Table V at both the current level of theory and at the B3LYP/6-311G** and CCSD͑T͒/6-311G** levels as reported by Cao et al 7 Finally, the relative energies, including the zero-point vibrational energies ͑ZPVE͒ for the QCISD/6-311G** level, can be found in Table V and are illustrated in Fig. 9.…”

“…The calculations of the ground state potential energy surface of C 2 H 2 FO by Cao et al 7 also do not include a dissociation pathway to this channel, although they reported a bimolecular transition state corresponding to FϩH 2 CCO→HFϩHCCO direct hydrogen abstraction.…”

“…7 As shown in Table V, the isomerization transition state, TS1, has been calculated to lie approximately 2.19 eV above the ground state, or 1.48 eV above the CH 2 FϩCO products, while the dissociation barrier, TS2, is 1.19 eV above the ground state, or 0.48 eV above channel ͑1͒. TS1 is too high and TS2 is too low to generate P(E T ) distributions peaking at 0.5 eV.…”

“…2 Calculations of optimized geometries and vibrational frequencies for the X and B states of CH 2 CFO using the complete active space self-consistent field ͑CASSCF͒ method established that the observed band was the result of exciting the B state. 3 Spectral assignments, aided by measured dispersed fluorescence spectra, revealed excitation of the 3 ͑C-O stretch͒, 4 ͑CHH scissor͒, 5 ͑C-F stretch͒, 6 (CH 2 rock͒, 7 ͑C-C stretch͒, 8 ͑FCO bend͒, and 9 ͑CCO bend͒ modes of the B state. 1,6 The LIF study by Furubayashi et The heats of formation used to obtain the heats of reaction for channels ͑1͒-͑3͒, ͑5͒, and ͑6͒ are listed in Table I, while the heat of reaction for channel ͑4͒ is obtained from the theoretical work by Cao et al 7 The energy level diagram for CH 2 CFO and these product channels is presented in Fig.…”

“…20 Grußdorf et al 19 have shown that the main products are CH 2 20 while the HCCOϩHF channel was attributed to direct H-atom abstraction. 18,19 Recently, a detailed theoretical study of the C 2 H 2 FO radical potential energy surface by Cao et al 7 at the B3LYP/6-311G** and CCSD͑T͒/6-311G** levels yielded barrier heights for numerous ground state dissociation pathways. Additionally, this work showed that the transition states ͑TS͒ leading to channels ͑1͒, ͑3͒-͑6͒ lie below the excitation energies involved in the B 2 AЉ←X 2 AЉ transition.…”