Wavelength effects in the ultraviolet-laser ablation of polycarbonate and poly(α-methylstyrene) examined by time-of-flight mass spectroscopy

Slow moving material (velocity ≊3×104 cm/s) ejected from polycarbonate and poly(α-methylstyrene) targets by ultraviolet laser photoablation is probed using time-of-flight mass spectroscopy. The product distribution seen from polycarbonate, using resonant-two-photon ionization with 248- or 266-nm light, consists of aromatic species smaller than the monomer. Mass spectra are similar for 355-, 266-, and 193-nm ablation, and the products differ structurally from the starting material; both observations suggest that slow moving species are ejected by a thermal mechanism at all three wavelengths. 248-nm ablation of polycarbonate near the ablation threshold, gives a different product distribution and it is argued that a cooler thermal regime is being sampled or, that photochemical effects are important. The dominant product seen in 266-, 248-, and 193-nm ablation of poly(α-methylstyrene) is the monomer in each case. Subtle differences present in the resulting mass spectra may be due to photochemical effects, but major similarities suggest that slow movers are ejected by a photothermal mechanism.