Sufficient quantities of mass-selected cations have been isolated in inert matrices for vibrational spectroscopic observation for the first time. When 15-25-nA beams of CF3+ from CF3Cl, CF3Br, or CF3H are co-deposited for 10-25 h with neon or argon at 5 K, the antisymmetric stretching vibration (v(3)) of the cation can be observed by FTIR spectroscopy. The mechanism by which the matrix maintains the necessary approximate neutrality is not certain; however, both positive and negative charges are detected when the matrices containing mass-selected cations are allowed to warm.