Vibrational predissociation in the bending levels of the $Ã$ state of C₃Ar

Vibrational predissociation (VP) has been observed in 16 bands of the C₃Ar van der Waals complex near the 0 v₂ 0 – 000 (v₂ = 2⁻, 4⁻, 2⁺) and 0 2⁻ 2 − 100 bands of the $Ã$¹Π–$X̃$¹Σ⁺_g system of C₃. New higher resolution wavelength-resolved emission (WRE) spectra covering a wider spectral range have been recorded for many of these C₃Ar bands, which show that most of the features observed in fluorescence must be reassigned as emission from the C₃ fragment. Two types of VP processes have been recognized. The first type gives rise to vibrationally hot C₃ fragments, mostly following |Δv| = 1, |ΔP| = 1 propensity rules, where P is the vibronic angular momentum of C₃. The second type gives vibrationally cooled fragments. The VP processes can change abruptly from one type to the other with comparatively small differences in vibrational energy. Although the initial states are associated with both orbital components of the C₃, $Ã$¹Π_u state, most of the VP fragments belong to the lower orbital component. A dipole-induced dipole model has been used to interpret the observed ΔP- propensities. Ab initio calculations of the binding energies of the ground and excited electronic states of C₃Ar have been carried out; the calculated values are consistent with estimates of ≤144 cm⁻¹ and 164 cm⁻¹, respectively, given by the WRE spectra.