The B̃2Σu+→X̃2Πg spectrum of CO2+ was recorded at a low rotational temperature (⋍20 K) in a crossed molecular beam/electron beam apparatus. The low J (J < 20.5) levels of the B̃ state are strongly perturbed. Due to the low temperature of the source, for the first time it was possible to assign transitions from these perturbed levels. Extra branches originating from both e and f levels of the upper state are observed. A three-level interaction (involving probably two vibronic levels of the Ã2Πu state) is suggested to explain the experimental observations.