H atom produced in the thermal decomposition of CH
3OH highly diluted in Ar (0.48−10 ppm) was monitored behind reflected shock
waves by atomic resonance absorption spectrometry (ARAS) at fixed temperatures (and pressures), that is, 1660 (1.73 atm), 1760 (2.34 atm), 1860 (2.04 atm), 1950 (2.18 atm), and 2050 K (1.76 atm) (±10 K, respectively). High sensitivity for the H atom has been attained by signal averaging of the ARAS signals down to the concentrations of 1 × 10
11 atoms/cm
3 and enables us to determine the branching fraction for the direct H atom production channel, CH
3OH → CH
2OH + H (channel
1c) in a mixture of 1 ppm CH
3OH. Channel
1c is confirmed to be minor, that is, branching fraction for channel
1c is expressed by Log(
k1c/
k1) = (− 2.88 ± 1.88) × 10
3/
T − (0.23 ± 1.02), which corresponds to
k1c/
k1 < 0.03 for the present temperature range. By using 0.48 and 1.0 ppm CH
3OH with (100−1000) ppm H
2, the total decomposition rate
k1 for CH
3OH → products is measured from the time dependence of H atom, where the radical products of main channels
1a and
1b, that is, OH, CH
3, and CH
2, were
converted rapidly into H atoms. The experimental result is summarized as Log(
k1/cm
3molecule
−1s
−1) = (−12.82 ± 0.71) × 10
3/
T − (8.5 ± 0.38). A theoretical study based on ab initio/TST calculations with high accuracy has been conducted for the reaction:
3CH
2 + H
2 → CH
3 + H (reaction
3). The rate is given by
k3/cm
3molecule
−1 s
−1 = (7.32 × 10
−19)
T2.3 exp (−3699/
T). This result is used for numerical simulations to evaluate
k1. Present experimental results on the thermal decomposition rate of CH
3OH are found to be consistent with previous works. It is also found that time dependence of [H] observed in the 10 ppm CH
3OH in Ar can be reproduced very well by kinetic simulations by using a reaction mechanism composed of 36 elementary reactions.