FORMATION OF BETA-FLUOROETHYL RADICAL AND CLOSED-SHELL PRODUCTS IN REACTIONS OF PHOTOGENERATED FLUORINE-ATOMS WITH ETHENE IN SOLID ARGON

Solid-state reactions of F atoms with ethene molecules were initiated by UV photolysis of dilute solutions of F-2 and C2H4 in solid Ar. Prod ucts stabilized in the matrix were detected by infrared spectroscopy. Experiments were conducted at different temperatures in order to disti nguish reactions in matrix-isolated F-2-C2H4 complexes (at 16 K) from reactions of diffusing thermal F atoms (at 26 K). Comparison with the kinetic EPR data (Benderskii, V. A. et al. Mendeleev Commun. 1995, 6, 245) permitted the identification of the infrared spectrum of the beta -fluoroethyl radical, which is the main product of the F + C2H4 reacti on. Frequencies and absolute absorption intensities of the eight stron gest infrared bands of beta-C2H4F are reported. Photolysis of isolated F-2-C2H4 complexes forms the closed-shell products C2H3F-HF and trans - and gauche-1,2-C2H4F2 with relative yields 0.6:0.2:0.2. Successive a ddition of two thermal F atoms to an isolated C2H4 molecule forms only the two conformers of 1,2-C2H4F2. The difference between product bran ching ratios of the latter reaction and the direct photoinduced reacti on of F-2-C2H4 complexes is qualitatively explained by the difference in size of the reaction cages and excess energies of the vibrationally excited intermediate (C2H4F2).