Hickson, Kevin M.
Spada, Rene F. K.
Vichietti, Rafael M.
Machado, Francisco B. C.
Haiduke, Roberto L. A.
Total Authors: 7
 Univ Bordeaux, ISM, F-33400 Talence - France
 Inst Tecnol Aeronaut, Dept Fis, Sao Jose Campos, BR-12228900 Sao Paulo - Brazil
 Inst Tecnol Aeronaut, Dept Quim, Sao Jose Campos, BR-12228900 Sao Paulo, SP - Brazil
 Univ Sao Paulo, Inst Quim Sao Carlos, Dept Quim & Fis Mol, BR-13566590 Sao Paulo, SP - Brazil
Total Affiliations: 4
Journal of Physical Chemistry A;
DEC 24 2020.
Web of Science Citations:
The rates of numerous activated reactions between neutral species increase at low temperatures through quantum mechanical tunneling of light hydrogen atoms. Although tunneling processes involving molecules or heavy atoms are well known in the condensed phase, analogous gas-phase processes have never been demonstrated experimentally. Here, we studied the activated CH + CO2 -> HCO + CO reaction in a supersonic flow reactor, measuring rate constants that increase rapidly below 100 K. Mechanistically, tunneling is shown to occur by CH insertion into the C-O bond, with rate calculations accurately reproducing the experimental values. To exclude the possibility of H-atom tunneling, CD was used in additional experiments and calculations. Surprisingly, the equivalent CD + CO2 reaction accelerates at low temperature as zero-point energy effects remove the barrier to product formation. In conclusion, heavy-particle tunneling effects might be responsible for the observed reactivity increase at lower temperatures for the CH + CO2 reaction, while the equivalent effect for the CD + CO2 reaction results instead from a submerged barrier with respect to reactants. (AU)