The dynamics of the autoionization reactions of simple molecules (water, hydrogen sulphide, and ammonia) by collision with helium and neon metastable atoms has been studied analyzing the kinetic energy spectra of the emitted electrons (by PIES - Penning Ionization Electron Spectroscopy) obtained in our laboratory in a crossed beam experiment at a collision energy of 20 meV. These spectra are compared and discussed with the photoelectron spectra measured using He(I) and Ne(I) photons in the same experimental conditions, and with previous PIES spectra obtained in our laboratory for the same systems at higher collision energies (70 and 55 meV for thermal collisions involving He* and Ne* atoms, respectively). In this way, the negative energy shifts for the formation of [Rg---H2O]+, [Rg---H2S]+ and [Rg---NH3]+ ionic complexes in their accessible electronic states (where Rg = He, Ne) are obtained and discussed. A unified analysis of new and old data indicates that in the case of He* and Ne*-M (where M = H2O, H2S, NH3) the autoionization dynamics is strongly stereo selective depending on the features of the transition state [Rg---M]* of such reactions, as: i) the anisotropic intermolecular potentials characterizing the approach between the incoming Rg*-M collisional partners; ii) the preferential geometry giving rise to the reaction; and iii) the involved molecular orbitals in the autoionization mechanism. In general, autoionization reactions are fast reactions playing an important role in thermal plasmas, electrical discharges, for the production of laser systems, and in the chemistry of planetary ionospheres. Despite the role of ionic species in planetary atmospheres and interstellar medium is well known, only recently the autoionization reactions were proposed as an important ions source formation on Earth, Mars and Mercury upper atmospheres.
Photo- and Penning- ionization electron spectroscopy of simple molecules: A comparative study to characterize the transition state of autoionization reactions
Falcinelli Stefano
2018
Abstract
The dynamics of the autoionization reactions of simple molecules (water, hydrogen sulphide, and ammonia) by collision with helium and neon metastable atoms has been studied analyzing the kinetic energy spectra of the emitted electrons (by PIES - Penning Ionization Electron Spectroscopy) obtained in our laboratory in a crossed beam experiment at a collision energy of 20 meV. These spectra are compared and discussed with the photoelectron spectra measured using He(I) and Ne(I) photons in the same experimental conditions, and with previous PIES spectra obtained in our laboratory for the same systems at higher collision energies (70 and 55 meV for thermal collisions involving He* and Ne* atoms, respectively). In this way, the negative energy shifts for the formation of [Rg---H2O]+, [Rg---H2S]+ and [Rg---NH3]+ ionic complexes in their accessible electronic states (where Rg = He, Ne) are obtained and discussed. A unified analysis of new and old data indicates that in the case of He* and Ne*-M (where M = H2O, H2S, NH3) the autoionization dynamics is strongly stereo selective depending on the features of the transition state [Rg---M]* of such reactions, as: i) the anisotropic intermolecular potentials characterizing the approach between the incoming Rg*-M collisional partners; ii) the preferential geometry giving rise to the reaction; and iii) the involved molecular orbitals in the autoionization mechanism. In general, autoionization reactions are fast reactions playing an important role in thermal plasmas, electrical discharges, for the production of laser systems, and in the chemistry of planetary ionospheres. Despite the role of ionic species in planetary atmospheres and interstellar medium is well known, only recently the autoionization reactions were proposed as an important ions source formation on Earth, Mars and Mercury upper atmospheres.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
