Final Defense

Robert Stevens, UT-Austin

"Alignment Effects of Hydrogen Reflection by Si(100)"

3:00pm, RLM 5.104

Abstract: Previous scattering experiments have shown a dependence of reflectivity on the alignment of the angular momentum vector of molecular hydrogen incident on a surface of Pd(111), Isakson 2001. In these past experiments orthohydrogen was preferentially aligned relative to the surface by preparing the J=3 state. This J=3 state has multiple values for its m_J quantum number and therefore there is a distribution in J=3 alignment. Within I will discuss the design of a new laser that can efficiently pump parahydrogen from the J=0 state, which has no distribution in m_J and therefore the resulting J=2 state can be aligned with much better precision. Evidence suggests (Isakson, 2001) that the perpendicular alignment of the angular momentum vector with respect to the surface (helicopter-type motion) was less reflective than the parallel alignment (cartwheeler-type motion) for orthohydrogen when interacting with Pd(111). Within a study of the preservation of these alignments, both helicopter and cartwheeler, for J=3 and J=2 initial states will be studied as they reflect off of the unreactive Si(100) surface. This study will strongly influence future studies, ones off of reactive surfaces such as Pd(111), and dictate if loss of alignment can explain the perceived decreased reflectivity.