Infrared (IR) absorption spectra of matrix-isolated HCCCH2 have been measured. Propargyl radicals were generated in a supersonic pyrolysis nozzle, using a method similar to that described in a previous study (Jochnowitz, E. B.; Zhang, X.; Nimlos, M. R.; Varner, M. E.; Stanton, J. F.; Ellison, G. B. J. Phys. Chem. A 2005, 109, 3812-3821). Besides the nine vibrational modes observed in the previous study, this investigation detected the HCCCH2 (X) over tilde B-2(1) out-of-plane bending mode (nu(8)) at 378.0 (+/-1.9) cm(-1) in a cryogenic argon matrix. This is the first experimental observation of nu(8) for the propargyl radical. In addition, seven overtone and combination bands have also been detected and assigned. Ab initio coupled-cluster anharmonic force field calculations were used to guide the analysis. Furthermore, nu(12), the HCCCH2 in-plane bending mode, has been assigned to 333 (+/-10) cm(-1) based on the detection of its overtone (2 nu(12), 667.7 +/- 1.0 cm(-1)) and a possible combination band (nu(10) + nu(12), 1339.0 +/- 0.8 cm(-1)). This is the first experimental estimation of nu(12) for the propargyl radical.