Atmospheric Chemistry of Methyl Isocyanide-An Experimental and Theoretical Study

Simen Gjelseth Antonsen; Arne Joakim C Bunkan; Tomas Mikoviny; Claus J Nielsen; Yngve Stenstrøm; Armin Wisthaler; Erika Zardin

doi:10.1021/acs.jpca.0c05127

Atmospheric Chemistry of Methyl Isocyanide-An Experimental and Theoretical Study

J Phys Chem A. 2020 Aug 13;124(32):6562-6571. doi: 10.1021/acs.jpca.0c05127. Epub 2020 Jul 30.

Authors

Simen Gjelseth Antonsen¹, Arne Joakim C Bunkan², Tomas Mikoviny², Claus J Nielsen², Yngve Stenstrøm¹, Armin Wisthaler², Erika Zardin²

Affiliations

¹ Department of Chemistry, Biotechnology and Food Science, P.O. Box 5003, NO-1432 Aas, Norway.
² Section for Environmental Sciences, Department of Chemistry, University of Oslo, P.O. Box 1033 - Blindern, 0315 Oslo, Norway.

Abstract

The reaction of CH₃NC with OH radicals was studied in smog chamber experiments employing PTR-ToF-MS and long-path FTIR detection. The rate coefficient was determined to be k_CH₃NC+OH = (7.9 ± 0.6) × 10^-11 cm³ molecule^-1 s^-1 at 298 ± 3 K and 1013 ± 10 hPa; methyl isocyanate was the sole observed product of the reaction. The experimental results are supported by CCSD(T*)-F12a/aug-cc-pVTZ//M06-2X/aug-cc-pVTZ quantum chemistry calculations showing the reaction to proceed primarily via electrophilic addition to the isocyanide carbon atom. On the basis of the quantum chemical data, the kinetics of the OH reaction was simulated using a master equation model revealing the rate coefficient to be nearly independent of pressure at tropospheric conditions and having a negative temperature dependence with k_OH = 4.2 × 10^-11 cm³ molecule^-1 s^-1 at 298 K. Additional quantum chemistry calculations on the CH₃NC reactions with O₃ and NO₃ show that these reactions are of little importance under atmospheric conditions. The atmospheric fate of methyl isocyanide is discussed.