Low-Energy Electron Attachment to the Dichlorodifluoromethane (CCl₂F₂) Molecule

Abstract

Results from a joint experimental study of electron attachment to dichlorodifluoromethane (CCl(2)F(2)) molecules in the gas phase are reported. In a high resolution electron beam experiment involving two versions of the laser photoelectron attachment method, the relative cross section for formation of the dominant anion Cl(-) was measured over the energy range 0.001-1.8 eV at the gas temperature T(G) = 300 K. It exhibits cusp structure at thresholds for vibrational excitation of the nu(3)(a(1)) mode due to interaction with the attachment channels. With reference to the thermal attachment rate coefficient k(T = 300 K) = 2.2(8) x 10(-9) cm(3) s(-1) (fitted average from several data), a new highly resolved absolute attachment cross section for T(G) = 300 K was determined. Partial cross sections for formation of the anions Cl(-), Cl(2)(-), F(-), ClF(-), and CCl(2)F(-) were measured over the range 0-12 eV, using three different electron beam experiments of medium energy resolution. The dependence of the attachment rate coefficient k(T(e);T(G) = 300 K) on electron temperature T(e) was calculated over the range 50-15 000 K, based on a newly constructed total cross section for anion formation at T(G) = 300 K. R-matrix calculations for Cl(-) production have been carried out for comparison with the experimental data. The R-matrix results are in line with the main experimental observations and predict the dependence of the DEA cross section on the initial vibrational level nu(3)() and on the vibrational temperature. Furthermore, the cross section for vibrational excitation of the nu(3) mode has been computed.

Electron attachment to molecules in a cluster environment

“…b) Present address: Dipartimento di Chimica e Chimica Industriale, Università di Pisa, Via Risorgimento 35,56126 Pisa,Italy. to find the attachment amplitudes and calculate DEA cross sections for two halocarbon molecules, CF 2 Cl 2 and CF 3 Cl, embedded in water clusters. DEA for both molecules was studied in the gas phase, [21][22][23] and the developed theoretical models are consistent with experimental observations. Both molecules attach electrons at low energies due to electron capture into the lowest unoccupied molecular orbital (LUMO) of the a 1 symmetry.…”

“…Note that the results are presented only for the ground vibrational state, therefore the zero-energy peak is not due to higher-excited states which are present at increased vibrational temperature. 23 To clarify the origin of this effect, in Fig. 7 we plot the resonance width as a function of electron energy for the equilibrium nuclear geometry.…”

“…Accordingly, the DEA cross section peaks at a much lower energy and exhibits an additional zero-energy peak at room temperature due to contributions from excited vibrational states. 23 In the present paper, we use these results to modify electron attachment amplitudes in the presence of water clusters. We are looking at general trends treating the CF 2 Cl 2 and CF 3 Cl molecules in the presence of the water trimers and hexamers.…”

On the Classical Coupling between Gravity and Electromagnetism

“…While it can be experimentally challenging to work with electrons at this energy, there are, for example, electron-molecule collision experiments that readily operate at or near this regime [38]. In the absence of any force, a 1 MeV electron would take 53 μs to travel 1 m. Now, consider this same electron at the Earth's surface.…”

On the relation between the activation energy for electron attachment reactions and the size of their thermal rate coefficients

“…As experimental database we use critically chosen rate coefficients at room temperature for a selection of closedshell halogenated hydrocarbon molecules which span a wide range of activation energies (up to about 0.7 eV). 5,6,[8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27] We emphasize that for DEA systems with large activation energies rate coefficients at room temperature are very small; thus they are difficult to measure directly, and impurities in the molecular sample have to be assessed with great care.…”