Laser-induced decomposition of dimethyl cadmium on a quartz substrate

Abstract

The photochemistry of adsorbed dimethyl cadmium at submonolayer levels on a fused quartz surface has been investigated at 193 and 248 nm using a rare-gas fluoride excimer laser. The desorbed gaseous products, which include CH 2, CH 3, CH 4, C 2H 4, C 2H 5, C 2H 6, Cd, CH 3Cd and (CH 3) 2Cd, have been detected by time-of-flight mass spectrometry with either electron impact or resonance-enhanced multiphoton ionization. The translational energies of these desorption products could be characterized in terms of Maxwell-Boltzmann temperatures, T MB ‘ s , which depend strongly on sample dosage (surface coverage), laser fluence and photon energy. The T MB ‘ s of the C 1 and C 2 hydrocarbon species were found to be much lower than those of Cd, CH 3Cd and (CH 3) 2Cd, suggesting that the electronic excitation/relaxation mechanism may be involved in the desorption of Cd and Cd-containing species. The rotational temperature of the CH 3 radical, determined by analysis of REMPI spectra, was found to be much colder than its translational temperature. A realistic mechanism is proposed for the UV-photochemistry of adsorbed (CH 3) 2Cd.