Methanediol
formed by the hydrolysis of formaldehyde is an important
intermediate in the formation of formic acid in the atmosphere. However,
the formation of methanediol by the direct reaction of formaldehyde
(HCHO) with water (H2O) is not feasible in the gas phase
in the atmosphere due to the very high enthalpy of activation at 0
K for the HCHO + H2O reaction. Here, by using quantum chemical
methods and reaction rate theory, we report a new mechanistic route
for the iodic acid-catalyzed gas-phase hydrolysis of formaldehyde.
The present findings show that iodic acid serves as an excellent catalyst
in this reaction, decreasing the enthalpy of activation at 0 K from
36.01 kcal/mol for the HCHO + H2O reaction to −13.28
kcal/mol for the HCHO + H2O + HIO3 reaction
with respect to the separate reactants. Additionally, the calculation
results also show that water can catalyze the HCHO + HIO3 reaction, decreasing the enthalpy of activation at 0 K for the HCHO
+ HIO3 reaction from 2.96 to −10.00 kcal/mol. The
calculated kinetics results reveal that the gas-phase hydrolysis of
formaldehyde catalyzed by iodic acid can make a substantial contribution
to the sink of formaldehyde and the formation of methanediol below
260 K. The reaction of formaldehyde with iodic acid catalyzed by water
dominates over the HIO3 + OH reaction under full atmospheric
conditions. The present findings are expected have broad implications
for understanding the formation of methanediol and the sink of formaldehyde
and iodic acid in the atmosphere.