Abstract: The A2Πu-X2Πg electronic absorption spectrum of the Cl2+ molecular cation in the region between 16820 and 17350 cm-1 was observed by employing optical heterodyne magnetic rotation enhanced velocity modulation spectroscopy. Cl2+ is a paramagnetic molecule; however, the intensities of some spectral lines, belonging to three bands whose origins are near 17282, 17324 and 16913 cm-1, respectively, remain unchanged with in the magnetic field. This indicates that both the upper and lower states have a weak Zeeman effect. The Zeeman contribution is nearly zero for the 2Π1/2 state, while nonvanishing for the 2Π3/2 state. Therefore, this behavior for the spectral assignment of Cl2+, including its isotopics was utilized and the identity of these bands was confirmed as members of the Ω=1/2 component of the electronic transition conveniently and unambiguously. The assigned bands are the (3, 7) band of the Ω=1/2 component of 35Cl+2 and 35Cl37Cl+ and the (2, 7) band of the Ω=1/2 component of 35Cl2+. It extends the range of vibrational assignments considerably in both the ground and the excited state, and leads to the successful rotational analysis. New molecular constants of Cl2+ were obtained from the observed line positions, band by band, using a weighted leastsquares fitting procedure.