Efficient ArF laser production and detection of carbon atoms from simple hydrocarbons

Excimer lasers are currently being utilized as a means of photofragmentation and fragment excitation for chemical detection purposes. In the case of small hydrocarbons, this phenomenon is generally not well characterized and is poorly understood. Experiments aimed at a better understanding of the interaction of simple carbon-containing molecules with the ArF (193-nm) excimer laser and at exploring the potential analytical applications of this process are described. Specifically, carbon atoms were generated by multiphoton photolysis of CO, CH(4), C(2)H(2), C(3)H(8), CH(3)OH, and CH(3)COCH(3) using the ArF laser. Their presence was detected by two sensitive methods, laser-induced fluorescence (LIF) and resonance ionization emission spectroscopy (RIES), both of which take advantage of the coincident overlap between the ArF laser and the(1)D(2) ? (1)P(1)(0) transition at 193.1 nm with emission detection at 247.9 nm. The RIES method detects single photons resulting from the photolytically produced carbon ion recombination and relaxation processes. An enhancement in the RIES signal was observed when a second tunable laser pulse operating at 247.9 nm followed the ArF laser pulse. Both methods not only offer sensitive detection of the photolytic precursor molecules but also require only relatively simple experimental apparatus. Detection levels for the precursor molelcule considerably lower than 10(11)/cc for LIF and 10(12)/cc for RIES can be estimated based on the observed rates of signal production.