A New Insight on Stereo-Dynamics of Penning Ionization Reactions.

Recent developments in the experimental study of Penning ionization reactions are presented here to cast light on basic aspects of the stereo-dynamics of the microscopic mechanisms involved. They concern the dependence of the reaction probability on the relative orientation of the atomic and molecular orbitals of reagents and products. The focus is on collisions between metastable Ne(P) atoms with other noble gas atoms or molecules, for which play a crucial role both the inner open-shell structure of Ne and the HOMO orbitals of the partner.

Penning ionization electron spectroscopy of hydrogen sulfide by metastable helium and neon atoms.

The dynamics of the Penning ionization of hydrogen sulfide molecules by collision with helium and metastable neon atoms, occurring in the thermal energy range, has been studied by analyzing the energy spectra of the emitted electrons obtained in our laboratory in a crossed beam experiment. These spectra are compared with the photoelectron spectra measured by using He(I) and Ne(I) photons under the same experimental conditions. In this way we obtained the negative energy shifts for the formation of H2S(+) ions in the first three accessible electronic states by He*(2(3,1)S1,0) and Ne*((3)P2,0) Penning ionization collisions: the 2b1 (X̃(2)B1) fundamental one, the first 5a1 (Ã(2)A1), and the second 2b2 (B̃(2)B2) excited states, respectively.

The stereodynamics of the Penning ionization of water by metastable neon atoms.

The stereodynamics of the Penning ionization of water molecules by collision with metastable neon atoms, occurring in the thermal energy range, is of great relevance for the understanding of fundamental aspects of the physical chemistry of water. This process has been studied by analyzing the energy spectrum of the emitted electrons previously obtained in our laboratory in a crossed beam experiment [B. G.

Dissociative double photoionization of benzene molecules in the 26-33 eV energy range.

A time-of-flight mass spectrometer with a position sensitive ion detector was used to study the dissociative double ionization of benzene by UV synchrotron radiation. The threshold energy for the main dissociative processes, leading to CH(3)(+) + C(5)H(3)(+), C(2)H(3)(+) + C(4)H(3)(+) and C(2)H(2)(+) + C(4)H(4)(+) ion pairs were characterized by exploiting a photoelectron-photoion-photoion-coincidence technique, giving 27.8 ± 0.

Experimental and theoretical evidence of charge transfer in weakly bound complexes of water.

We report the definitive assessment of a measurable (half a kJ/mol) charge-transfer (CT) component in the interaction of water with the noble gases. The CT is found to be strongly stereoselective and is mediated by a highly asymmetric, donor/acceptor concerted role of the two hydrogen atoms, which can in fact dictate the equilibrium geometry of the adducts. This finding may be of general relevance in explaining the known peculiar orientational features of water's interactions.

Penning ionization of N2O molecules by He*(2(3,1)S) and Ne*(3P2,0) metastable atoms: theoretical considerations about the intermolecular interactions.

A theoretical investigation of the intermolecular interaction, operative in collision complexes of He*(2 3S1), He*(2 1S0), and Ne*(3P2,0) with N2O, is carried out to explain the main results of the experimental study reported in the preceding paper. The analysis is carried out by means of a semiempirical method based on the identification, modeling, and combination of the leading interaction components, including the effect of the selective polarization of the more external electronic cloud of the metastable atom in the intermolecular electric field. These and other crucial aspects of our approach have been quantitatively verified by ab initio calculations.

Penning ionization of N2O molecules by He*(2(3,1)S) and Ne*(3P2,0) metastable atoms: a crossed beam study.

The energetics of [Rg...

Low-lying electronic states of HBr2+.

The present study describes the characterization of energy and structure of HBr(2+) in its low-lying electronic states, achieved through an extension of a new empirical method [Chem. Phys. Lett.

Threshold-photoelectron-spectroscopy-coincidence study of the double photoionization of HBr.

A threshold-photoelectron-coincidence spectrum of HBr has been recorded in the 32.2-35.8 eV photon energy range, with a resolution of approximately 0.