AUTHOR=Pietanza Lucia Daniela , Colonna Gianpiero , Capitelli Mario 

TITLE=Dissociative Electron Attachment From Vibrationally Excited Molecules in Nanosecond Repetitively Pulsed CO Discharges and Afterglows

JOURNAL=Frontiers in Chemistry

VOLUME=7

YEAR=2019

URL=https://www.frontiersin.org/journals/chemistry/articles/10.3389/fchem.2019.00163

DOI=10.3389/fchem.2019.00163

ISSN=2296-2646

ABSTRACT=<p>Non-equilibrium vibrational distributions and electron energy distributions of CO in nanosecond repetitively pulsed (NRP) discharges and afterglows have been determined from a coupled solution of the time dependent Boltzmann equation for the electron energy distribution function (eedf) of free electrons and the master equations for the vibrational distribution function (vdf) of CO and the electronic excited states of CO and O and C atoms. Emphasis is given to the role of dissociative electron attachment (DEA) from vibrationally excited states in affecting the eedf and vdf under extreme conditions, i.e., an optically thick plasma with quenching processes involving the electronic excited states, populated by a sequence of discharge pulses and corresponding afterglows. In particular, the quenching process of the a<sup>3</sup>Π electronic state of CO determines a pumping of vibrational quanta in the ground state, which in turn largely modifies the CO vdf promoting the activation of DEA process. DEA rate coefficients have been obtained by using a complete set of vibrational (v) dependent cross sections through the <italic>CO</italic><sup>−</sup>(<italic>X</italic><sup>2</sup>Π) channel and by using the experimental <italic>v</italic> = 0 cross section of Rapp and Briglia, which should include the contribution of other <italic>CO</italic><sup>−</sup> resonant states. The importance of the last contribution has been also estimated by using a scaling law to extend the <italic>v</italic> = 0 cross section over all the vibrational ladder of CO. In particular, this mechanism becomes competitive with the other reactive channels for very short inter-pulse delay times, i.e., the <italic>t</italic><sub><italic>id</italic></sub> = 1 μ<italic>s</italic>, being less important for longer inter-pulse delay times, i.e., the <italic>t</italic><sub><italic>id</italic></sub> = 25 μ<italic>s</italic>.</p>