Ultraviolet-laser photolysis of disilane

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Abstract
A combination of optical probing techniques, including time-resolved emission spectroscopy, dye-laser absorption spectroscopy, laser-induced fluorescence, and intracavity laser spectroscopy (ILS), have been used to investigate the reaction paths for the ArF excimer laser (193 nm, 6.4 eV/photon) photolysis of disilane, Si2H6. The experiments were carried out in an ultrahigh vacuum system into which Si2H6 was introduced at pressures ranging from 1 to 10 mTorr. Optical emission due to the Si 1P→1S and SiH A2Δ→X2Π transitions was observed with intensity rise times, following the laser pulse, of less than 100 ns, the experimental resolution. This indicates that for the pressures used in these experiments, Si and SiH were generated purely photolytically rather than through collisional processes. The maximum intensities of the Si and SiH peaks were measured as a function of ArF laser-beam photon flux density Jhν. SiH2 was never detected, up to the highest Jhν values used, 4×1017 photons/cm2 pulse, even though with ILS, the most sensitive of the optical-absorption techniques, we were able to detect absorption peaks assignable to rotational transitions in the (020)–(000) vibronic bands of the à 1B1←X̃ 1A1 electronic transition during Si2H6 pyrolysis at ∼350 °C. Based upon these experimental results, a model for the ultraviolet-laser photolysis of Si2H6 was developed involving a three-step cascade one-photon absorption process.