PHOTODISSOCIATION OF ADSORBED TRIMETHYLINDIUM

The photochemistry of trimethylindium (TMI) adsorbed on a quartz substrate at 150 K has been studied by time of flight mass spectrometry (TOF/MS) using electron impact ionization and resonance-enhanced multiphoton ionization techniques. Photolysis of adsorbed TMI at 222 nm results in the deposition of indium metal on the surface and the ejection of neutral and ionic fragments into the gas phase. The gas-phase photofragments observed were the neutral products In(CH3)2, InCH3, In, and CH3 and the ions In+, CH3+, and In(CH3)+. The neutral product distribution observed from photolysis on the surface was significantly different from the reported distribution observed in gas-phase photolysis of similar metal alkyls, M(CH3)3 (M = Al, Ga). The neutral product TOF profiles were characterized by Maxwell-Boltzmann temperatures which were different for each photoproduct. Ions formed on the surface did not desorb with Maxwell-Boltzmann velocity distributions and had significantly higher kinetic energies (2 eV), suggesting the instantaneous presence of a high electric field during the laser-induced photodissociation on the surface. As the surface coverage of In(CH3)3 was increased, a gradual increase in the neutral product translational energies was observed. The increase in the product kinetic energy was associated with photodecomposition of adsorbed TMI clusters of increasing size on the surface.