Radiative lifetimes of electronically excited states of N2O+, NO, O2+, CO+, and CO are measured by means of the phase-shift method. Excitation is performed by a modulated electron beam. Phase references are derived from He I, N2+, and CO+ transitions as well as from another independent method based on the very short decay time of the air fluorescence. Measurements are performed on the transitions N2O+ (B2 ∑u+ ➝ X2 IIg), NO (A2 ∑+ ➝ Χ2 II), O2+ (b4 Σg- ➝ a4 IIu), O2+ (A2 IIu ➝ X2 IIg), CO+(B2 ∑ ➝ X2 ∑), CO+ (B2 ∑ ➝ A2 II) , CO+ (A2 II ➝ X2 ∑), CO (b3 ∑+ ➝ a3 II), CO (B1∑+ ➝ A1 II). As far as feasable lifetimes of individual vibrational levels are measured. From the pressure dependence of the decay rates cross-sections for the quenching of the excited states by the parent molecules are obtained.