We report variational calculations of a large number of vibrational states of HCO2 and the H ... CO2 transition state for J = 0 using the code MULTIMODE and a realistic six degree-of-freedom potential energy surface. State-dependent rotational constants for both species are calculated for the same sets of vibrational states from exact rotation/vibration calculations for J = 1. The results of these variational calculations are used to obtain RRKM rate constants for the decomposition of HCO2 to form H + CO2. Comparison is made between these nonseparable RRKM results and those obtained from a standard, separable harmonic oscillator/rigid rotor evaluation of the RRKM rate constant expression. Significant differences between the nonseparable and separable results are found.