J. Phys. Chem. B 101 (1997) 2267-2276. Inner-Shell Excitation Spectroscopy of Polymer and Monomer Isomers of Dimethyl Phthalate S. G. Urquhart^† A. P. Hitchcock,*^,† A. P. Smith,^‡H. Ade^‡ and E. G. Rightor^§ ^†Department of Chemistry McMaster University, Hamilton, Ontario, Canada L8S 4M, ^‡Department of Physics, North Carolina State University, Raleigh, North Carolina 27695 ^§Analytical Sciences, B-1470, Dow Chemical Freeport, Texas 77541

Received: October 31, 1996; In Final Form: January 10, 1997

The C ls X-ray absorption spectra (XAS) of poly(diallyl phthalate), polydiallyl isophthalate), and poly-(ethylene terephthalate) (PET) have been recorded using transmission detection. The phthalate segments of these polymers are isomers with different patterns of substitution (ortho, meta, para) of the methyl carboxylate groups on the phenyl ring. The C ls and O is electron energy loss spectra (EELS) of the corresponding isomeric monomers, dimethyl phthalate dimethyl isophthalate and dimethyl terephthalate, have also been recorded in the gas phase using innelastic electron scattering under conditions dominated by electric dipole transitions. Good agreement is found in overall shape and in the energies of the spectral features of the same isomer in monomeric (EELS) versus polymeric (XAS) form. Ab initio calculations are used to provide a detailed interpretation of the spectra, in particular the origin of the isomeric variations. The analytical potential for using inner shell excitation spectroscopy to identify isomeric character and to map spatial distributions of polymer isomeric substitution is assessed.