G3MP2B3 calculations have been performed to investigate the potential energy surface for the reaction of thiophene with NO3 radical. Both direct hydrogen abstraction pathways and addition-elimination pathways have been found. The reaction is shown to start with an exothermic barrierless addition of NO3 to the double bond of thiophene ring to give thiophene-ON(O) O intermediate (IM1), possibly, IM1A and IM2. Intermediate IM1 can generate various products including P5 + NO2, P4 (C(S) HCH=CHC(O)H) + NO2, P6 (C(S) HCH=CHC(H) ONO2), and P3 + H. The most energetically favorable channel is found to be the formation of P5 by loss of NO2 from intermediate IM1. The calculations are inconsistent with the available experimental results. (C) 2008 Elsevier B. V. All rights reserved.