Photofragment Translational Spectroscopy of Fluorinated Halomethanes

Abstract

The primary and secondary dissociation processes of CF2Br2 and CF2BrI have been studied by photofragment translational spectroscopy in a pulsed molecular beam. The photolysis of CF2Br2 at 193 nm produces mainly the fragment pair CF2Br + Br and, in a competing primary process, CF2 + Br2. The CF2Br radicals are formed with sufficient internal energy to overcome the barrier of the unimolecular secondary dissociation to CF2+ Br. The photodissociation of CF2BrI at 248 nm also proceeds along two decay pathways involving the fission of the weak C‐I bond and the stronger C‐Br bond, respectively. The former reaction produces spin‐orbit excited iodine atoms I(2P1/2) and stable CF2Br radicals, whereas the latter reaction produces unstable CF2I radicals. The results of this study are compared with those of other workers, and an account of the ultraviolet photochemistry of fluorinated halomethanes is given.

Micropatterning MoS2/Polyamide Electrospun Nanofibrous Membranes Using Femtosecond Laser Pulses

“…Also, no broad band feature appeared in the spectrum for wavenumbers higher than 700 cm −1 , due to the luminescence present when the number of layers decreased [46], indicating the presence of multilayer MoS2 flakes in our sample, as expected [47]. 2g , A 1g and E 2 2g (not seen in Figure 3) are a result of vibrational modes within the MoS 2 layer [43]. The E 1 2g and A 1g modes of the exfoliated MoS 2 nanosheets were centered at 379 cm −1 and 404 cm −1 , respectively [44].…”

“…The sample was excited with laser light at 633 nm (1.96 eV), which closely matches the energy of the direct bandgap of MoS2 at room temperature [42]. Four first-order Raman active modes dominate the resonant Raman spectrum of MoS2, in which E1g, E 1 2g, A1g and E 2 2g (not seen in Figure 3) are a result of vibrational modes within the MoS2 layer [43]. The E 1 2g and A1g modes of the exfoliated MoS2 nanosheets were centered at 379 cm −1 and 404 cm −1 , respectively [44].…”

Avoided Curve Crossing between the A1 and B1 States in CF2Br2 Photolysis at 234 and 265 nm

“…Photodissociation studies of CF 2 Br 2 have been performed at 193 and 248 nm using the rotatable mass spectrometric technique. 4,5 The radical channel was the only observed primary photodissociation channel in the 248-nm photolysis experiments, while both the radical and the molecular elimination channels were observed at 193 nm. The bromine atom product quantum yield obtained by fluorescence detection at 222 nm has been found to be 1.63, suggesting the presence of three-body dissociation channel after excitation in the center of the A-band.…”

“…Three primary channels, i.e., radical (R1), molecular elimination (R2), and three-body dissociation channels (R3), are attainable energetically in the A-band. [3][4][5][6][7][8][9][10][11] The CF 2 Br radical formed through the radical channel can undergo further photodissociation (R4) or unimolecular decay of internally hot radicals (R5).…”

Matrix isolation and computational study of isodifluorodibromomethane (F2CBr–Br): A route to Br2 formation in CF2Br2 photolysis

“…This was first shown for photolysis at 193 nm in a molecular beam by Huber and co-workers. 17 Later, in ion imaging experiments, Park et al 8 reported a "trace" amount of Br 2 photoproduct following excitation at 234 nm. More recently, Lin and co-workers 5 probed Br 2 directly using cavity ring down spectroscopy, and reported a quantum yield of 0.04 for the molecular channel at 248 nm.…”