By employing the high-resolution pulsed field ionization-photoelectron (PFI-PE)-photoion coincidence method, we have examined the unimolecular dissociation reaction of energy-selected C2H3Br+ to form C2H3++Br near its threshold. The analysis of the breakdown curves for C2H3Br+ and C2H3+ yields a value of 11.9010+/-0.0015 eV for the 0 K dissociative photoionization threshold or appearance energy (AE) for C2H3+ from C2H3Br. This AE(C2H3+) value, together with the ionization energy (IE) for C2H3Br (9.8200+/-0.0015 eV) obtained by PFI-PE and threshold photoelectron (TPE) measurements, has allowed the determination of the 0 K dissociation energy (D-0) for the C2H3+-Br bond to be 2.081+/-0.002 eV. The 0 K AE(C2H3+) from C2H3Br obtained in this study corresponds to DeltaH(f0)()(C2H3+)=1123.7+/-1.9 kJ/mol. Combining the latter value and the known DeltaH(f0)()(C2H3)=306.7+/-2.1 kJ/mol, we calculated a value of 8.468+/-0.029 eV for the IE(C2H3), which is in accord with the result obtained in the previous photoionization efficiency study. We have also carried out high-level ab initio calculations for the IE(C2H3) at the Gaussian-3 and the CCSD(T,full)/CBS level of theory. The CCSD(T,full)/CBS prediction of 8.487 eV for the IE(C2H3-->bridged-C2H3+) is in good agreement with the IE(C2H3) value derived in the present experiment. Combining the 0 K AE(C2H3+)=11.9010+/-0.0015 eV and the IE(C2H3)=8.468+/-0.029 eV yields the value of 3.433+/-0.029 eV for D-0(C2H3-Br). We have also recorded the TPE spectrum of C2H3Br in the energy range of 9.80-12.20 eV. Members (n=5-14) of four autoionizing Rydberg series converging to the C2H3Br+((A) over tilde (2)A(')) state are observed in the TPE spectrum. The analysis of the converging limit of these Rydberg series and the vibrational TPE bands for C2H3Br+((A) over tilde (2)A(')) has provided more precise values for the nu(6)(+) (1217+/-10 cm(-1)) and nu(8)(+) (478+/-8 cm(-1)) modes and the IE (10.9156+/-0.0010 eV) for the formation of C2H3Br+((A) over tilde (2)A(')) from C2H3Br. (C) 2004 American Institute of Physics.