Adsorbate alignment in surface halogenation: standing up is better than lying down.

Bromine atom transfer to a silicon surface as a function of physisorbed adsorbate alignment (see picture: left, vertical 1-bromopentane; right, horizontal 1-bromopentane) of 1-bromopropane and 1-bromopentane on Si(111)-7×7 has been studied by STM. In both thermal and electron-induced bromination reactions, the vertical alignment is more reactive.