AVS 52nd International Symposium
    Surface Science Tuesday Sessions
       Session SS1-TuM

Paper SS1-TuM7
RAIRS Signature of the Ordered Methyl Bromide Monolayer on Pt(111)

Tuesday, November 1, 2005, 10:20 am, Room 202

Session: Vibrational Spectroscopy of Surfaces
Presenter: I. Samanta, University of Virginia
Authors: I. Samanta, University of Virginia
T. Schwendemann, University of Virginia
T. Kunstman, University of Essen, Germany
I. Harrison, University of Virginia
Correspondent: Click to Email
Scanning tunneling microscopy (STM) reveals that methyl bromide (CH@sub 3@Br) adsorbed on a Pt(111) surface can order into a relatively close packed monolayer of upright molecules even though the dipole moment of these rod-like molecules is substantial (1.8 Debye in the gas phase). The formation kinetics of the ordered (3 x 5) structure can be slow at temperatures less than 100 K. The unit cell contains four CH@sub 3@Br molecules of two kinds oriented with C-Br axis along the surface normal. The CH@sub 3@Br saturation coverage is estimated to be 0.27 ML by STM. Other ordered structures are observed at lower coverages. The evolution of ensemble-averaged reflection absorption infrared spectroscopy (RAIRS), thermal programmed desorption (TPD) spectroscopy, and photochemical dynamics experiments on CH@sub 3@Br/Pt(111) as a function of coverage will be discussed in light of the microscopic structures observed by STM. The RAIRS signature of the ordered CH@sub 3@Br monolayer is the disappearance of the @nu@@sub 5@ asymmetric CH@sub 3@ deformational mode near 1411 cm@super -1@ and the adsorption-site induced splitting of the @nu@@sub 2@ symmetric CH@sub 3@ deformational mode into a doublet at 1271 cm@super -1@ and 1277 cm@super -1@ with fwhms of just 3 cm@super -1@.