AVS 47th International Symposium
    Surface Science Wednesday Sessions
       Session SS-WeP

Paper SS-WeP28
Evidence for Two Chain Length Distributions in the Polymerization of Formaldehyde on Cu(100)

Wednesday, October 4, 2000, 11:00 am, Room Exhibit Hall C & D

Session: Poster Session
Presenter: T.R. Bryden, Michigan State University
Authors: T.R. Bryden, Michigan State University
S. Garrett, Michigan State University
Correspondent: Click to Email
The adsorption of formaldehyde on Cu(100) has been studied using electron energy loss spectroscopy (EELS) and temperature programmed desorption (TPD). At 85 K, formaldehyde (H@sub 2@CO) spontaneously polymerized to form a monolayer of poly(oxymethylene) (POM). Thermal decomposition/desorption of the polymer monolayer occurred via two kinetically different routes, producing two peaks in TPD that can be attributed to molecular H@sub 2@CO generated via depolymerization of the polymer. The presence of two polymer desorption peaks has not been previously observed in studies of formaldehyde adsorption on metal surfaces. The zero and first order features observed are attributed to chain length differences present between the species and can be explained using rate equations describing the production of monomer. Our data seems to indicate the number of chains, for the zero order species, is fixed while the degree of polymerization is changing as the amount of POM formed increases. EELS spectra, taken as a function of anneal temperature, indicate the two species are similar and show losses due to POM. However, the losses due to POM for the second species are lower in intensity and new modes are identified that are attributed to the end groups of the polymer, which is consistent with shorter chains. Additionally, the second species is more ordered relative to the mixture, which could account for the enhanced production of the first species during dosing experiments where the surface is covered with the second species during exposure to H@sub 2@CO.