Rotational state distribution of molecularly chemisorbed H on Pd(210)

Ueta, Hirokazu   ; Sasakawa, Yuya*; Ivanov, D.*; Ono, Satoshi*; Fukutani, Katsuyuki

On a flat metal surface, hydrogen typically chemisorbs dissociatively. On the other hand, it is known that hydrogen can molecularly chemisorbs on stepped surfaces, such as Ni(510) and Pd(210), in which the potential is expected to be highly anharmonic, unlike the case of physisorption. The anisotropic potential would modify the rotational state of H and promote ortho-para (o-p) conversion. For the system of H/Pd(210), a previous study with rotational-state-selective temperature programmed desorption indicated the occurrence of fast o-p conversion. In this study, to further probe the rotational state and conversion of molecularly chemisorbed H, a combination of photo-stimulated desorption and resonance-enhanced multiphoton ionization techniques is used. It is found that photo-desorbed H consists of a variety of rotational states with an anisotropic angular distribution. Photo-desorption and o-p conversion process will be discussed.