Pulsed laser single-photon ionization time-of-flight mass spectrometry is used to investigate the etch products resulting from thermal etching of Si(100) with molecular chlorine over a temperature range of 1023-1373 K and a pressure range of 10(-5)-10(-4) Pa. In this regime, two thermal etch products, SiCl2 and SiCl, are directly observed by ionization without fragmentation using 118 nm light. Over this temperature and pressure range, the desorption fluxes of SiCl2 and SiCl are proportional to the dosing chlorine pressure. A phenomenological activation energy of 0.36+/-0.03 eV is observed for the SiCl desorption flux from an Arrhenius plot. The SiCl2 product flux exhibits a complex temperature dependence, first. increasing and then decreasing, and thus this rate is controlled by at least two pathways. One pathway in the lower temperature regime may be a direct desorption channel. The other process at higher temperatures may be a competing reaction that limits the precursor species, most likely SiCl, for the formation of SiCl2 on the surface. The ability to detect the radical species without mass spectral cracking provides the potential to unravel such complex pathways.