The low-energy paths for the reaction of HO with C2H4 have been studied at the PMP2/aug-cc-PVQZ//MP2/cc-PVTZ level of theory. The rate constants for the production of C2H4OH, CH2CHOH + H and C2H3 + H2O calculated with variational RRKM theory indicated that below 500 K, the formation of C2H4OH (k(1)) via an OH...pi complex with 1.9 kcal/mol binding energy is the major product channel exhibiting a negative-temperature dependence; between 800 and 1000 K, the formation of CH2CHOH + H (k(2)) and C2H3 + H2O (k(3)) becomes competitive; at T > 1000 K, k(3) becomes dominant. k(1) was found to be strongly affected by multiple reflections above the well of the OH... n complex. The predicted results are in close agreement with available experimental data. (c) 2005 Elsevier B.V. All rights reserved.