HYDROGEN-BONDING AND MOLECULAR-ORIENTATION IN WATER FLUORINE ADLAYERSON SILVER(110)

The orientation and hydrogen bonding interactions of water coadsorbed with atomic fluorine on Ag(110) were examined with high resolution ele ctron energy loss spectroscopy (HREELS) and time-of-flight measurement s of electron stimulated desorption ion angular distribution (TOF-ESDI AD). Water exhibits four stabilized adsorption states in the presence of fluorine, identified as the B, A(1), A(2), and A(3) states in order of their decreasing desorption temperatures. The B state interacts wi th fluorine through one hydrogen bond with the other hydrogen remainin g free as evidenced by an O-H stretching frequency of 3700 cm(-1). Wat er molecules in the A(1) state interact through two strong hydrogen bo nds in a ratio of one water molecule per fluorine atom and cause a (2 X 1) to (1 X 2) surface phase transition of fluorine. Surprisingly, TO F-ESDIAD measurements detect no H+ emission from either the B or A(1) states indicating that all hydrogens are either pointed towards the su rface or far enough away from the surface normal to escape detection b y ESDIAD. Instead, emission of only high mass ions (O+/OH+/H2O+/F+) oc curs in two beams along the [1(1) over bar0$] direction for the B stat e and along the [001] direction for the combined B + A(1) states. The A(2) and A(3) states of water hydrogen bond to the B and A(1) states a nd exhibit vibrational spectra that approach that of ice, although the interaction with fluorine remains sufficiently strong to impart measu rable spectral differences.