A relative rate experiment is carried out for six isotopologues of methanol and their reactions with OH and Cl
radicals. The reaction rates of CH2DOH, CHD2OH, CD3OH, 13CH3OH, and CH3
18OH with Cl and OH radicals
are measured by long-path FTIR spectroscopy relative to CH3OH at 298 ( 2 K and 1013 ( 10 mbar. The OH
source in the reaction chamber is photolysis of ozone to produce O(1D) in the presence of a large excess of molecular
hydrogen: O(1D) + H2 f OH + H. Cl is produced by the photolysis of Cl2. The FTIR spectra are fitted using a
nonlinear least-squares spectral fitting method with measured high-resolution infrared spectra as references. The
relative reaction rates defined as R ) klight/kheavy are determined to be: kOH + CH3OH/kOH + 13CH3OH ) 1.031 ( 0.020,
kOH + CH3OH/kOH + CH3
18OH ) 1.017 ( 0.012, kOH + CH3OH/kOH + CH2DOH ) 1.119 ( 0.045, kOH + CH3OH/kOH + CHD2OH )
1.326 ( 0.021 and kOH + CH3OH/kOH + CD3OH ) 2.566 ( 0.042, kCl + CH3OH/kCl + 13CH3OH ) 1.055 ( 0.016, kCl + CH3OH/
kCl + CH3
18OH ) 1.025 ( 0.022, kCl + CH3OH/kCl + CH2DOH ) 1.162 ( 0.022 and kCl + CH3OH/kCl + CHD2OH ) 1.536 (
0.060, and kCl + CH3OH/kCl + CD3OH ) 3.011 ( 0.059. The errors represent 2s from the statistical analyses and do not
include possible systematic errors. Ground-state potential energy hypersurfaces of the reactions were investigated
in quantum chemistry calculations at the CCSD(T) level of theory with an extrapolated basis set. The 2H, 13C, and
18O kinetic isotope effects of the OH and Cl reactions with CH3OH were further investigated using canonical
variational transition state theory with small curvature tunneling and compared to experimental measurements as
well as to those observed in CH4 and several other substituted methane species.
Udgivelsesdato: 16 August 2008