Hydroxymethyl Radical Self-Recombination in High-Temperature Water

作者：Kanjana Kotchaphan; Walker Jonathan A; Bartels David M^*

来源：Journal of Physical Chemistry A, 2015, 119(10): 1830-1837.

DOI：10.1021/jp510029p

The self-recombination reaction of (CH2OH)-C-center dot radicals in neutral aqueous solution has been studied at temperatures up to 300 degrees C at a pressure of 220 bar using pulse radiolysis and transient absorption. CH2OH species decay by second-order kinetics independent of the applied dose, with a rate constant at 22 degrees C of 2k = 1.4 +/- 0.1 x 10(9) M-1 s(-1). The recombination follows Arrhenius behavior with the activation energy (E-a) 12.7 +/- 0.9 kJ/mol and pre-exponential factor of 1.9 +/- 0.4 x 10(11) M-1 s(-1). The overall recombination is significantly slower than the diffusion limit at elevated temperature, meaning that both disproportionation and dimerization channels have significant activation barriers. Ab initio calculations support the inference that the dimerization channel has no energy barrier, but has a large negative activation entropy barrier. The disproportionation channel (giving aqueous formaldehyde) almost certainly involves one or more specific water molecules to lower its activation energy relative to the gas phase.

• 出版日期2015-3-12