Quantitative tunneling spectroscopy study of molecular structural changes due to electron irradiation

We have developed a new technique (utilizing inelastic electron tunneling spectroscopy) for the study of changes in molecular structure due to 30-keV electron irradiation. Analysis and interpretation of our experiments is done through the following: (1) an algorithm for fitting observed spectra with a series of fundamental peaks and thereby quantitatively provides the actual intensity of each peak; (2) a theory that determines the total (primary and secondary) electron fluence in the vicinity of the molecules and through the use of theoretical dissociation cross sections provides estimates of effective dissociation cross sections. Thus contributions of various molecular and geometrical properties to the degradation process can be delineated. Experimental data for $\beta -D-\mathrm{fructose}$ reveals that CH, ${\mathrm{CH}}_2$ bonds are less susceptible to molecular degradation than the bonds in the COH functional group; also double bonds are formed. The strength and limitation of this technique are discussed.