Regular Article

Gas phase Boudouard reactions involving singlet–singlet and singlet–triplet CO vibrationally excited states: implications for the non-equilibrium vibrational kinetics of CO/CO₂ plasmas

¹ Laboratório Associado de Plasma (LAP), Instituto Nacional de Pesquisas Espaciais (INPE)/MCT, CP 515, São José dos Campos, São Paulo, CEP 1224 7-9 70, Brazil
² Universidade de Brasìlia, Instituto de Fisica, Brasìlia, Brazil
³ Università di Perugia, Dipartimento di Chimica, Biologia e Biotecnologie, 06123 Perugia, Italy
⁴ Consiglio Nazionale delle Ricerche, Istituto di Struttura della Materia, 00016 Roma, Italy
⁵ NANOTEC – Istituto di Nanotecnologia – Consiglio Nazionale delle Ricerche, 70126 Bari, Italy
⁶ Purdue University School of Aeronautics and Astronautics, West Lafayette, IN 47907, USA

^a e-mail: federico.palazzetti@unipg.it

Received: 14 February 2017
Received in final form: 8 June 2017
Published online: 19 October 2017

Abstract

Rate constants for the Boudouard reactions: CO + CO → CO₂ + C and CO + CO → C₂O + O, involving ground and vibrationally excited states for both singlet–singlet and singlet–triplet reactant CO molecules, have been obtained by using the transition-state theory on an ab initio generated potential energy surface. The dependence of the activation energies for the different processes on the vibrational energy of reactants has been estimated through a parametrization that accounts for the utilization of vibrational energy and is calculated by the forward and backward ab initio activation energies of the relevant processes at zero vibrational energy. The results and their comparison with available experimental reaction rates demonstrate the importance of vibrational excitation not only for the singlet–singlet reactions, but also for the singlet–triplet ones, which are here investigated for the first time. Finally, the implications of the present results on the kinetics of CO/CO₂ cold plasmas are discussed: for their modeling the temperature dependence of the obtained rates for singlet–singlet and singlet–triplet reactants in the ground vibrational states have been represented by both Arrhenius and deformed Arrhenius equations.