One of the challenges for calculating the electronic structure of HCCX cations is that the X and A states have the same electronic state symmetry. Consequently, calculations of the A state with conventional density functional methods and single reference correlated wavefunctions such as coupled clusters (CC) would collapse to the X state. CASSCF (complete active space self-consistent field) and CASPT2 (CASSCF with second order perturbation theory) are appropriate methods but the active space must be carefully selected for each individual molecule. It would be highly desirable to have a straight-forward, "black-box" method that can treat the ground state and excited states of radical cations with the same accuracy and that does not need to be customized for each molecule. EOMCCSD-IP (equation of motion coupled cluster with single and double excitations and ionization) is potentially such a "black-box" method that is similar in accuracy to calculations with CCSD (CC with single and double excitation) and is more efficient than CCSD for radical cations. In this formalism, calculations of open shell cations start with a CCSD calculation of the closed shell neutral molecule. The wavefunctions for the ground and excited states of the radical cation are then generated using an equation of motion approach involving single ionization and single excitations of the coupled cluster wavefunction for the neutral molecule. For reviews of coupled cluster methods such as CCSD, EOMCCSD and EOMCCSD-IP see references 24-26. In a previous study, we investigated the angular dependence of strong field ionization in HCCX (X = F, Cl, Br, I). In recent work we simulated charge migration and decoherence in HCCI + with timedependent configuration interaction (TDCI) using geometries and vibrational frequencies for the X and A states of HCCI cation available in the literature. In the present work we have calculated the structures, ionization potentials and vibrational frequencies of HCCX cations in the X and A states with CCSD and EOMCCSD-IP using a cc-pVTZ basis set. The calculated data will be used in future simulations of charge migration and decoherence in these systems.