Laser-excitation study of triplet CO

Abstract

Metastable CO a³Π(v= 0) molecules, at concentrations near 10⁸–10⁹ cm^–3, were produced by the reaction Ar³P_2,0+CO₂→ CO a³Π+ O + Ar. Narrow-band excitation with a dye laser was used to form the d³Δ state of CO, which was observed through fluorescence of the d–a transition. Rotationally-resolved d–a laser-excitation spectra are reported.

Lifetime measurements of the d³Δ state were made from fluorescence decays, following initial excitation of the v= 5 and 4 vibrational levels. The zero-pressure lifetime of CO d³Δ(v= 4) was 5.75 ± 0.70 µs.

Vibrational relaxation of CO d³Δ(v= 4) in collisions with Ar was found to be efficient, with a probability of ca. 10^–2. Relaxation is believed to occur by collisional curve-crossing, probably to the e³Σ^– state, rather than by V–T transfer. Lifetime data on d³Δ(v= 5) support the existence of a strong, rotationally-dependent perturbation in the Ω= 1 component of this state.