In low-energy electron impact on neutral molecules, the free electron and the molecule often form an intermediate metastable electron-molecule compound. [1][2][3] This compound may either release the excess electron by autodetachment (AD) [1] or fragment by a reaction called dissociative electron attachment [DEA, Eq. (1)]: [1][2][3] e À þ AB ! ðABÞA wide variety of chemical transformations initiated by electron impact can be attributed to DEA. [1][2][3] In particular, it is well known that in organic molecules DEA efficiently leads to bond dissociation, producing radical and radical-anion molecular fragments. In general, in all examples studied and understood theoretically, DEA leads to an anionic fragment and a neutral fragment. [1][2][3] Recently, mass spectroscopic measurements monitoring DEA of fructose have shown that several neutral fragments may appear in addition to the anionic fragment.[4] The underlying mechanisms have not been clarified yet, but it may be suspected from the detected products that the two fragments initially formed by DEA as in Equation (1) have further fragmented by several stepwise reactions. In any case, electron-molecule reactions are seen to be chemically rich and are of chemical interest.Herein we report on a new elementary reaction (i.e., single-step reaction) mechanism of an electron and a molecule in a metastable compound which we call (two or more) bond breaking by a catalytic electron (BBCE). Unlike in DEA, the formed compound anion dissociates into nonradical neutral molecular subunits and a free electron, which plays the role of a catalyst [Eq. (2)]:where we stress that at least two bonds (not a double bond) break in the elementary reaction path. Notice that the electron is freed in the course of the elementary reaction, that is, the electron is not attached to any of the chemical products of the elementary reaction and, thus, we refer to this mechanism as an electron-catalyzed mechanism. This elementary reaction involves both bond breaking and detachment of the electron. The key differences between BBCE and DEA are as follows: 1. More than one s bond (two-center bond) is broken in the elementary BBCE reaction. 2. The products formed in the BBCE are neutral. 3. The electron is released in the course of the elementary BBCE reaction.Below, we illustrate this mechanism more precisely by investigating electron impact on the quadricyclanone (QDCO) molecule. As will become clearer, the low-energy electron impact on QDCO can be viewed as proceeding via a compound negative ion metastable state. We have acquired considerable experience in the ab initio computation of energy and lifetime of metastable anions using non-Hermitian quantum chemical methods. [5][6][7] Recently, the introduction of a so-called continuum remover complex absorbing potential [8] and its implementation in Greens function methods [9] have made non-Hermitian quantum chemical methods applicable to larger systems. The efficient identification of the metastable states and the correct scaling of the electronic ener...

No abstract

A potential energy model is developed for calculating proton affinities and relating them to inner-shell electron binding energies, The model is based on the Hellmann-Feynman theorem and employs CND0/2 wave functions. A linear correlation is found between proton affinities and inner-shell binding energies within a homologous series of molecules. The proposed model is applied here to interpret the substituent effects, particularly those of alkyl groups, on proton affinities. The correlation between proton affinities and inner-shell binding energies can be interpreted in terms of a potential model because of similar relaxation effects upon addition of a proton or ionization of a core electron; i.e., both processes can be described as the addition of a positive charge to a localized region of the molecule. The variation in binding energy of the nonbonding (highest occupied) orbital in aliphatic amines, alcohols, and ethers cannot be explained simply in terms of the relaxation potential model; ground state effects are of comparable magnitude here.alculations of proton affinities and binding energies C of inner-shell electrons are closely related. In both cases one calculates an energy difference between species which differ primarily in the amount of charge they bear. One species may be considered to be derived from the other by the addition of a positive charge (or abstraction of a negative charge) to a particular nuclear center. The energy need for this must be strongly affected by the potential energy at the nuclear center. According to classical electrostatics, the change in energy with charge is the electrostatic potential. It is not surprising, then, that attempts have been made to interpret proton affinities and ESCA binding energies in terms of the electrostatic potential at a nucleus.2 However, to our knowledge there has not yet appeared a quantitative model of proton affinities in terms of potentials. We present here such a model which, based on the Hellmann-Feynman theorem, gives a quantitative interpretation of chemical effects on proton affinities. Semiempirical (CND0/2)3 wave functions have been used to calculate the potentials rendering the model applicable to large molecules. The relationship between ESCA binding energies and proton affinities is derived and explicit correlations are presented. Basic FormalismBoth ESCA chemical shifts and proton affinities will be interpreted in terms of energy differences between isoelectronic molecules whose Hamiltonians differ only in the amount of nuclear charge at one center. The energy of state n will be called En and will be assumed (Born-Oppenheimer approximation) to take the form where { R e ) , represents the equilibrium nuclear coordinates for state n. We are interested in Eion -Eo,where Eion is the protonated or ionized state. For proton affinities it is assumed that AH* = Ei,, -Eo. Note that proton affinity is defined as -AHr, or Eo -( ( R e } n) + Envib + Enrot + EntrEns (1) E, = Enelectronic(1) Supported in part by the U.S. Army Research Office.Eion, an...

Low energy electrons can initiate and control chemical reactions through resonant attachment forming an electron-molecule compound state. Recently, it has been theoretically shown that free electrons can also act as catalysts in chemical reactions. We investigate this novel concept for the case of conversion of formic acid into CO. Resonant production of CO from cold formic acid films by low energy electron impact is observed using Fourier transform infrared spectroscopy. The resonant peak observed at 6 eV is identified as the catalytic electron channel. The experimental results are augmented with the quantum chemical calculations.