Is the C2H+H2O reaction anomalous?

B3LYP/6-311G(d,p), MP2/6-311G(d,p) and CCSD(T)/6-311+G(2d,2p) (single-point) methods are employed to investigate the doublet potential-energy surface of the C2H+H2O radical reaction, It is shown that the quasi-direct hydrogen abstraction leading to product C2H2+OH is kinetically much more competitive than other dissociation or association-elimination processes. Further higher-level CCSD(T)/6-311+G(3df,2p)//QCISD/6-311G(d,p)+ZPVE calculation predicts this simple H-abstraction process to possess a classical barrier height of 3.7 kcal/mol, which is larger than those for the C2H+H-2 and C2H+CH4. reactions. The calculated rate constants of the direct hydrogen abstraction process indicate that the title reaction is very slow near room temperature and may be of less importance than previously expected. Our results show that the C2H+H2O radical reaction is a normal quasi-direct hydrogen abstraction process in keeping with the Polanyi-Evans an type correlation between the k (295 K) value and the H-X bond dissociation energy (X=OH, H, CH3, and C2H5). However, our results are in sharp contradiction to the recent proposal based on the experimental measurements that the title reaction is quite fast and may have an association-elimination mechanism. This calls for future experimental investigations of this radical reaction.