Dissociative electron attachment to molecules in the gas phase and in rare gas solids

Abstract

Measurements of dissociative electron attachment (DEA) cross sections in chloroalkanes and chlorofluoromethanes have shown strong correlations between the peak DEA cross sections and the vertical attachment energies (VAEs) of these compounds. We explore the extent to which these gas phase data can be used to predict such cross sections for molecules embedded within or on the surface of a Kr solid. Effective VAEs are computed that include polarization of the solid by the anion and effects due to electron motion in the lattice. Comparisons are made with recent surface and bulk measurements and show good agreement for CF3Cl both within and on the surface. Satisfactory agreement is found for CH3Cl in the bulk but not on the surface.

Photochemistry of caged molecules: CD3Cl@Ice

“…Low-energy electrons generated this way subsequently attach to the CD 3 Cl molecules, forming an excited negatively charged ion, after traveling through the layers of ASW that can be considered a neutral spacer. 20,21 As was shown before, 23 one may expect that the DEA rate will be suppressed if the CD 3 Cl molecules are separated from the metal surface by gradually thicker ASW layers, while the direct photon absorption process should remain unchanged. In the current experiments 2-10 ASW spacer layers were deposited first, then a fixed amount of CD 3 Cl ͑0.6 ML͒, and then caging with an additional 10 ASW layers of water.…”

“…19 Other photoproducts that are formed inside the cage, such as CD 3 CD 3 ͑mass 36͒ follow a perturbed bimolecular channel, namely, ͑DEA͒. 20,21 Both mechanisms produce ''hot'' methyl and chlorine radicals, which lead to most of the chemistry we observe. An important difference between the two excitation mechanisms is the state of the nascent post-irradiation chlorine-in DEA it is a chloride anion, while in the direct photoabsorption process it is a chlorine radical.…”

“…The cross section found for the formation of ethane, for example, at photon energy of 6.4 eV, is smaller than those reported for the DEA of methyl chloride inside the solid matrix of krypton by more than two orders of magnitude. 20,21 It suggests that ASW as the caging material substantially suppress the overall DEA process and thus the photoreactivity that results from it. The observation that some of the products' formation rate saturate above a photon dosage of ϳ10 19 must relate to the question of whether a direct photochemical reaction takes place during the laser pulse, or is it a subsequent process that occurs following sample heating of the caged photofragments.…”

“…This number is smaller than those reported for the DEA of methyl chloride in a solid matrix of krypton by more than two orders of magnitude. 20,21 It suggests that cage walls made of ASW substantially suppress the overall DEA process and thus the photoreactivity that results from it. At a photon energy of 5.0 eV the cross sections are about an order of magnitude smaller than these at 6.4 eV.…”

Photochemistry of molecules at confined environment: CD3Br/O/Ru(001) and CO2@Ice

“…Studies in this field have included inter-and intra-molecular electron transfer, 6 transmission 7-9 conduction within and through molecular layers, [10][11] and dissociative electron attachment (DEA) processes. [12][13][14] Recent interest in molecular electronics has brought the basic science in this field closer to modern technology than ever before. [8][9][10] Based on the extensive research discussed above, it is interesting and surprising to note that in spite of the tremendous importance of electron-induced processes in chemical and biological systems, previous studies have not attempted to directly investigate molecular orientation dependence or stereochemistry in electronmolecule interactions.…”