Photodissociation and desorption of multilayer acetone on a Si(100) surface by 193 nm laser irradiation

Thermal desorption spectra of acetone on Si(100) were measured using a temperature programmed desorption (TPD) technique. Acetone molecules condensed on a Si(100) at 95 K desorbed at 133 K. The peak profile indicated a zeroth-order desorption mechanism. The desorption energy was estimated to be 47.6 ± 4 kJ/mol. Dissociation and desorption of the acetone molecules condensed on the surface by 193 nm pulsed laser irradiation were investigated with a quadrupole mass spectrometer using a time-of-flight technique. When high fluence laser pulses of 363 mJ/cm² were irradiated to a thick layer of acetone formed by an exposure of 1500 L, hyperthermal acetone molecules of about 2 eV were observed desorbing from the surface. Acetyl and methyl radicals formed by dissociation were also vaporized simultaneously. Thermal dissociation of acetone leading to 2CH₃ and CO as products occurred slowly after the laser irradiation. These dissociation processes are different from those in the gas phase.