Paper SS2-MoA7
Isotope-Specific Deposition of Vibrationally Excited Molecules

Monday, October 15, 2007, 4:00 pm, Room 611

Direct IR excitation of gas-phase reagents offers a potential means of isotope selective chemical vapor deposition (CVD). A narrow bandwidth IR laser selectively excites a vibrational mode in a single isotopomer of methane. These vibrationally excited molecules are significantly more reactive, enhancing their rate of deposition. Here we present results showing control of the carbon isotopic ratio of surface adsorbates by IR excitation of methane. We recombinatively desorb the methyl fragment deposited on a Ni(111) surface after methane dissociatively adsorbs on the surface. We are able to quantify the yield of both carbon-13 and carbon-12 using a mass spectrometer to measure ¹³CH₄ and ¹²CH₄ desorbing from the surface. Using a methane molecular beam with the natural abundance of carbon-13 and carbon-12, we are able to achieve an eight-fold enhancement in carbon-13 deposition by exciting less than 0.1% of the methane molecules in the molecular beam.