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 ind icated 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 irra diation were investigated with a quadrupole mass spectrometer using a time-of-flight technique. When high fluence laser pulses of 363 mJ/cm( 2) were irradiated to a thick layer of acetone formed by an exposure o f 1500 L, hyperthermal acetone molecules of about 2 eV were observed d esorbing from the surface. Acetyl and methyl radicals formed by dissoc iation were also vaporized simultaneously. Thermal dissociation of ace tone leading to 2CH(3) and CO as products occurred slowly after the la ser irradiation. These dissociation processes are different from those in the gas phase.