Near-infrared electronic spectrum of CH2+

Four vibronic bands of the à ²B₁(Π_u)←X∼_²A1 electronic transition of CH2+ have been observed in the near infrared from ∼11 000-13 000 cm^-1 using a highly sensitive spectrometer based on a Ti:sapphire laser and a positive column plasma. The two states are derived from the lowest ²Πu state of the linear conformation as a result of a strong Renner-Teller effect. As expected, the rovibronic structure of the CH2+ spectrum is very similar to that of the isoelectronic BH₂ radical reported by Herzberg and Johns. Results of a preliminary analysis are given in which the rotational structures of the two states are treated independently, the ground state as a near-prolate asymmetric rotor and the excited state as a linear molecule.