Near-edge study of molecular oxygen and nitrogen clusters on a krypton surface

${\mathrm{N}}_2$ or ${\mathrm{O}}_2$ clusters are condensed on Kr films at 20 K, and the K edge is studied using synchrotron radiation. For molecular nitrogen, little or no change is observed in the near-edge structure as one goes from the small cluster to the thin-film limit. For molecular oxygen, an increase is observed in the splitting of the ${\mathrm{\sigma }}^{\mathrm{*}}$ feature with increasing oxygen coverage. We attribute this phenomenon to local structural and electronic changes related to cluster growth. The splitting of the ${\mathrm{\sigma }}^{\mathrm{*}}$ feature for the smallest amount of oxygen deposited is larger than the gas-phase value, and we believe this latter result is due to the formation of molecular-oxygen dimers.