A theoretical investigation of the atmospherically important reaction between chlorine atoms and formic acid: Determination of the reaction mechanism and calculation of the rate coefficient at different temperatures

Maggie Ng, Kam Wah Mok, Edmond P F Lee, John M. Dyke

Research output: Journal article publicationJournal articleAcademic researchpeer-review

5 Citations (Scopus)

Abstract

The Cl + HCOOH reaction is important in the atmosphere, as the chlorine (Cl) atom is an important oxidant, especially in the marine boundary layer, and formic acid (HCOOH) is one of the most abundant organic acids in the troposphere. The reaction surfaces of the two H abstraction channels were computed by second-order unrestricted Møller-Plesset perturbation theory (UMP2) and density functional theory (DFT) calculations. Relative electronic energies were improved to the RCCSD(T)/CBS and UCCSD(T)-F12/CBS levels. The barrier of the C-H hydrogen abstraction channel was found to be lower by about 10 kcal mol-1. Rate coefficients (k) of this channel were calculated at different temperatures at various variational transition state theory (VTST) levels including tunnelling. For single-level direct dynamics VTST calculations, the computed k (2.5 × 10-13 cm3 molecule-1 s-1) using the BMK (Boese and Martin meta hybrid) functional at the highest level (ICVT/SCT) agrees the best with experimental values at 298 K (1.8 and 2.0 × 10-13 cm3 molecule-1 s-1). For dual-level direct dynamics calculations (RCCSD(T)/CBS//MP2 MEP), an adjusted barrier height of 3.1 kcal mol-1 is required to match the ICVT/SCT k with the experimental values. The computed rate coefficients of the Cl + HCOOH reaction is reported for the first time with a temperature range of 200-1500 K. The implications of the results obtained to atmospheric chemistry are discussed.
Original languageEnglish
Pages (from-to)1511-1533
Number of pages23
JournalMolecular Physics
Volume113
Issue number13-14
DOIs
Publication statusPublished - 1 Jan 2015

Keywords

  • ab initio calculation
  • atmospheric chemistry
  • Cl + HCOOH
  • rate coefficient calculation
  • transition state theory calculation

ASJC Scopus subject areas

  • Biophysics
  • Molecular Biology
  • Condensed Matter Physics
  • Physical and Theoretical Chemistry

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