Measurement of the Renner-Teller effect in X²Π CO₂⁺ by diode laser absorption

Abstract

Four vibronic components of the (v ₁, v ₂, v ₃) = (020) - (010) hot band of CO₂ ⁺ have been measured by infrared diode laser absorption spectroscopy. The CO₂ ⁺ molecules were generated in a hollow cathode discharge of a dilute mixture of CO₂ in helium at a total pressure of a few hundred mTorr. The hamiltonian operator for a linear triatomic molecule in a ²Π electronic state undergoing bending vibrational motion is described and the vibronic matrix elements given. The theory is used to fit the observed data together with previously reported infrared measurements of the bending fundamental and combination differences extracted from the electronic spectrum of the ion. The analysis yields rotational, spin-orbit, and vibronic parameters including those describing the Renner-Teller and Fermi resonance effects, and the bending potential function including anharmonicity.