The C2H3 + C2H4 reaction was studied using the laser photolysis/photoionization mass spectrometry technique at T = 625-950 K and bath gas (helium) densities of (6-12) x 10(16) atom cm(-3). Reaction rate constants can be described by the expression k(1) = 10(-11.69 +/- 0.44) exp(-(2830 +/- 790) K/T) cm(3) molecule(-1) s(-1). C4H6 and C4H7 were detected as primary products; thermal stability of C4H7 at 950 K indicates that it is a delocalized radical. The experimental results are compared with predictions obtained in master equation modeling based on the potential energy surface of Miller. (c) 2005 Elsevier B.V. All rights reserved.