The dissociation dynamics of energy selected i-C3H7X (X = H, Cl, Br, and I) ions have been investigated by imaging photoelectron-photoion coincidence (iPEPICO) spectroscopy using synchrotron radiation from the X04DB VUV beamline in the Swiss Light Source of the Paul Scherrer Institut. The 0 K dissociation energy (E-0) for i-C3H8 was determined to be 11.624 +/- 0.002 eV. This leads to a 298 K isopropyl ion heat of formation of 805.9 +/- 0.5 kJ mol(-1). The Delta H-f(298K)degrees(i-C3H7+) combined with the measured 0 K onsets for i-C3H7+ formation from isopropyl chloride (11.065 +/- 0.004 eV), isopropyl bromide (10.454 +/- 0.008 eV), and isopropyl iodide (9.812 +/- 0.008 eV) yields the 298 K isopropyl chloride, bromide, and iodide heats of formation of -145.7 +/- 0.7, -95.6 +/- 0.9, and -38.5 +/- 0.9 kJ mol(-1), respectively. These values provide a significant correction to literature values and reduce the error limits. Finally, the new i-C3H7+ heat of formation leads to a predicted adiabatic ionization energy for the isopropyl radical of 7.430 +/- 0.012 eV and a 298 K proton affinity for propene of 744.1 +/- 0.8 kJ mol(-1).