Origin of Resonant Character in the Electron Impact Two-Body Neutral-Fragmentation of Methane.

The observation of peaks in the threshold region of two-body neutral fragmentation of methane molecule, i. e., CH →CH +H, by low energy electron (LEE) impact has been an enigma.

A hitherto unknown stability of DNA basepairs.

The resonance capture of ubiquitous very low energy electrons (vLEEs) into the π* orbitals of nucleobases is a potential doorway to DNA damage. Our ab initio quantum chemical calculations reveal a possible protection function, which is specific to the complementary basepairing, against such vLEE induced DNA damage.

A Concerted Synchronous [2 + 2] Cycloreversion Repair Catalyzed by Two Electrons.

The current understanding of photoenzyme-catalyzed [2 + 2] cycloreversion repair of cyclobutane pyrimidine dimer (CPD) is that a photogenerated electron from the photolyase enzyme catalyzes the repair. This one-electron catalyzed repair is a sequential two-bond breaking cycloreversion of the cyclobutane center and involves a negative ion radical as an intermediate. Here, by resonantly capturing two exogenous low-energy electrons into the molecular field of a CPD, we show that the concerted synchronous two-bond breaking reaction, which is intermediate-free, and hence a safe repair, is feasible through two-electron catalysis.

Formation of CO from formic acid through catalytic electron channel.

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.

Inducing chemical reactivity on specific sites of a molecule using the Coulomb interaction exerted by a low energy electron.

Remarkable site-specificity in the resonant attachment of low energy electrons (LEEs) to molecular targets is proposed as an efficient method for inducing chemical reactivity on specific sites of molecules. The Coulomb interaction between the attached electron and the most polarizable molecular electrons localized on the attached site is the reason for site-specific chemical reactivity. The Coulombically induced site-specific chemical reactivity is best illustrated by the LEE induced chemical transformation of a weakly bound molecular complex into a strong covalent adduct.

Communication: Low-energy free-electron driven molecular engineering: In situ preparation of intrinsically short-lived carbon-carbon covalent dimer of CO.

Molecular modification induced through the resonant attachment of a low energy electron (LEE) is a novel approach for molecular engineering. In this communication, we explore the possibility to use the LEE as a quantum tool for the in situ preparation of short lived molecules. Using ab initio quantum chemical methods, this possibility is best illustrated for the in situ preparation of the intrinsically short-lived carbon-carbon covalent dimer of CO from a glyoxal molecule.

Low energy electron catalyst: the electronic origin of catalytic strategies.

Using a low energy electron (LEE) as a catalyst, the electronic origin of the catalytic strategies corresponding to substrate selectivity, reaction specificity and reaction rate enhancement is investigated for a reversible unimolecular elementary reaction. An electronic energy complementarity between the catalyst and the substrate molecule is the origin of substrate selectivity and reaction specificity. The electronic energy complementarity is induced by tuning the electronic energy of the catalyst.

Dissociative electron attachment studies on acetone.

Dissociative electron attachment (DEA) to acetone is studied in terms of the absolute cross section for various fragment channels in the electron energy range of 0-20 eV. H(-) is found to be the most dominant fragment followed by O(-) and OH(-) with only one resonance peak between 8 and 9 eV. The DEA dynamics is studied by measuring the angular distribution and kinetic energy distribution of fragment anions using Velocity Slice Imaging technique.

Low-energy-electron induced permanently reactive CO₂ molecules.

Ab initio quantum chemical studies show that a very weak molecular complexation of CO2 with a dipolar molecule is able to suppress the autoionization of the electron from its transient negative ion states. Since the autoionization is suppressed, the transient negative ion can efficiently relax its geometry to form the reductively activated CO2 moiety. Unlike the reductively activated isolated CO2 molecules, which are deactivated immediately due to their thermodynamic metastability, the reductively activated CO2 moieties of the weak molecular complexes are infinitely long-lived and, hence, permanently reactive.

O(-) from amorphous and crystalline CO2 ices.

O(-) desorbed from amorphous and crystalline films of CO2 at 18 K under low energy electron impact is studied using time of flight mass spectrometry. The nature of the CO2 film is characterized by Fourier transform infrared spectrometry as a function of film thickness. It is found that the desorption rate from amorphous films is considerably larger than that from crystalline films.

Optimization of nonlinear optical properties by substituent position, geometry and symmetry of the molecule: An ab initio study.

Static polarizability and first- and second-order hyperpolarizability tensors are computed at the correlated level for a series of para-nitroaniline derivatives. The importance of including electron correlation effects in the determination of equilibrium structure and the molecular properties is investigated. A qualitative description of the substitution effects, planarity, and symmetric effect of the molecule on the molecular susceptibility is discussed.

Odd-even oscillations in first hyperpolarizability of dipolar chromophores: role of conformations of spacers.

Quantum chemical calculations on the linear and nonlinear electric polarizabilities of dipolar molecules separated by the alkyl spacers have been performed on O(2)N-Ph-N=N-Ph-(CH(2))(n)-Ph-N=N-Ph-NO(2), n = 1-12. These molecules exhibit a very strong odd-even behavior in the first hyperpolarizabilities (beta), with large (small) beta for n = odd (n = even). Such odd-even oscillations have been reported experimentally on similar systems, but the origin of such phenomena remains unclear.